Hemp Husbandry

Robert A. Nelson

Internet Edition
Copyright 2000

Chapter 4  Table of Contents

Botany & Breeding

1. Classification
2. Botanical Description
3. Trichromes
4. Phenotypes
5. Genetics
6. Polyploidy
7. Breeding
8. Light
9. Sexual Expression
10. References.

4.1  ~ Classification

Class: Angiospermae
Subclass: Dicotyledonae
Superorder: Dilleniidae
Order: Urticales
Family: Cannabinaceae
Genus: Cannabis
Species: sativa, indica
Subspecies: sativa
Varieties: ruderalis, vulgaris, spontanea, gigantea, chinensis, etc.(1-4)

4.2 ~ Botanical Description

USDA botanist Lyster H. Dewey published this official "Botanical Study of Hemp" in 1913:

"THE PLANT --- The hemp plant, Cannabis sativa L., is an annual, growing each year from the seed. It has a rigid, herbaceous stalk, attaining a height of 1 to 5 meters (3 to 16 ft), obtusely 4-cornered, more or less fluted or channeled, and with well-marked nodes at intervals of 10 to 50 cm (4 to 20 in). When not crowded it has numerous spreading branches, and the central stalk attains a thickness of 3 to 6 cm (1 to 2 in), with a rough bark near the base. If crowded, as when sown broadcast for fiber, the fluted stems are without branches or foliage except at the top or on the shortened branches, appearing fascicled, are palmately compound and composed of 5 to 11 --- usually 7 --- leaflets. The leaflets are dark green, lighter below, lanceolate, pointed at both ends, serrate, 5 to 15 cm (2 to 6 in) long, and 1 to 2 cm (3/8 to 3/4 in) wide. Hemp is dioecious, the staminate or pollen-bearing flowers and the pistillate or seed-producing flowers being borne on separate plants. The staminate plants are borne in small axillary panicles, and consists of five greenish yellow or purplish sepals opening wide at maturity and disclosing five stamens which discharge abundant yellow pollen. The pistillate flowers are stemless and solitary in the axils of the small leaves near the ends of the branches, often crowded so as to appear like a thin spike. The pistillate flower is inconspicuous, consisting of a thin, entire, green calyx, pointed, with a slit at one side, but remaining nearly closed over the ovary and merely permitting the two small stigmas to protrude at the apex. The ovary is one seeded, developing into a smooth, compressed or nearly spherical achene (the "seed"), 2.5 to 4 mm (1/10 to 3/16 in) thick and 3 to 6 mm (1/8 to 1/4 in) long, from dark gray to light brown in color and mottled, The seeds cleaned for market nearly always include some still covered with green, gummy calyx. The seeds vary in weight from 0.008 to 0.027 gram, the dark-colored seeds being generally much heavier than the light-colored seeds of the same sample. The light-colored seeds are often imperfectly developed. Dark-colored and distinctly mottled seeds are generally preferred.

"The staminate plants are often called the flowering hemp, since the pistillate flowers are rarely observed. The staminate plants die after the pollen is shed, but the pistillate plants remain alive and green two months later, or until the seeds fully developed.

"THE STALK --- The hemp stalk is hollow, and in the best fiber-producing types the hollow space occupies at least one-half the diameter. The hollow space is widest, or the surrounding shell thinnest, about midway between the base and the top of the plant. The woody shell is thickened at each node, dividing the hollow space into a series of partly separated compartments. If the stalk is cut crosswise a layer of pith, or thin-walled tissue, is found next to the hollow center, and outside of this a layer of wood composed of hard, thick-walled cells. This layer, which forms the "hurds", is a very thin shell in the best fiber-producing varieties. It extends clear across the stem below the lowest node, and in large, coarse stalks grown in the open it is much thicker and the central hollow relatively smaller. Outside of the hard woody portion is the soft cambium, or growing tissue, the cells of which develop into the wood on the inside, or into the bast and the bark on the outside. It is chiefly through this cambium layer that the fiber-bearing bast splits away from the wood in the processes of retting and breaking. Outside of this cambium is the inner bark, or bast, comprising short, thin-walled cells filled with chlorophyll, giving it a green color, and long thick-walled cells, making the bast fibers. These bast fibers are of two kinds, the smaller ones (secondary bast fibers) toward the inner portion making up rather short, fine fibers, many of which adhere to the wood or hurds when the hemp is broken, and the coarser ones (primary bast fibers) toward the outer part, extending nearly throughout the length of the stalk. Outside of the primary bast fiber is a continuation of the thin-walled stalk, chlorophyll-bearing cells free from fiber, and surrounding all is the thin bark.

"THE FIBER --- The hemp fiber of commerce is composed of the primary bast fibers, with some adherent bark and also some secondary bast fiber. The bast fibers consist of numerous long, overlapping, thick-walled cells with long, tapering ends. The individual cells, almost too small to be seen by the unaided eye, are 0.015 to 0.05 mm (3/1000 to 12/1000 in) in diameter, and 5 to 55 mm (3/6 to 2-1/8 in) long. Some of the bast fibers extend through the length of the stalk, but some are branched, and some terminate at each node. They are weakest at the nodes." (5)


4.3 ~ Trichromes

Most of the aerial parts of cannabis, especially the female bracts, possess minute hairs, or trichromes, some of which excrete glistening drops of resin, so the flowers seem to shine with sticky amber dew which has a characteristic minty odor. It is thought that cannabis produces its resin as a protective measure against ultraviolet radiation, insects or water loss. Three types of trichromes occur on cannabis:

1) Bulbous and cappitate (sessile and stalked), resin-producing, glandular hairs on the flowers, leaves and stems;

2) Non-glandular hairs having no apparent function; 3) Crystoliths which resemble the non-glandular hairs, but are shorter and contain deposits of calcium carbonate. (6-8)

4.4 ~ Phenotypes

The expression of a trait in a plant strain is termed a phenotype. The interactions of genetic potential (genotypes) and environmental conditions (ecotypes) produce unique phenotypes. The phenotype system of distinguishing varieties reconciles many of the arguments about the species of hemp, all of which can be allocated to phenotypic groups. The phenotype system is based on the analysis of the relative amounts of cannabinoids: Tetrahydrocannabinol (THC), Cannabinol (CBN), and Cannabidiol (CBD). (9-13)

The Phenotype Ratio (PR) is calculated thus:
             % CBD

Phenotype I: The resin is composed primarily of THC. The fresh, manicured flowers contain more than 0.3% THC, and less than 0.5% CBD. Both the male and female plants produce large amounts of the resin. Phenotype-I plants usually originate from countries south of Latitude 30o N, where the tropical climate allows a long growing season. Often it is called Cannabis indica, the variety cultivated primarily for drug use.

Phenotype II: The resin contains approximately equal amounts of THC and CBD. This group is not sharply distinguished from P-III, but P-II plants usually contain more THC than do P-IIIs, and the females are more potent than the males. P-II hemp usually originates from countries north of Lat. 30o N, and it flowers early in the summer since it is adapted to temperate climes. P-II may represent hybridization between P-I and P-III.

Phenotype III: The resin contains primarily CBD (more than 0.5%) and less than 0.3% THC. The female produces more cannabinoids than does the male plant. P-III hemp usually originates north of Lat. 30o N, and is known as Cannabis sativa, cultivated primarily for fiber and seeds.

Phenotype IV: The resin may contain large amounts of THC, and traces of Cannabigerol Monomethyl Ether (CBGM) and Cannabiverol (CBV). P-IV hemp originates in northeast Asia, and usually is known as Cannabis ruderalis.

The phenotypes rich in THC always possess Cannabichromene (CBC), sometimes in large amounts. Phenotypes rich in CBD also contain CBC.

4.5 ~ Genetics

Cannabis has a haploid number of 1n=10; its somatic number is 2n=20. Some researchers have counted 2n=18 + (XX) or (YY). In the male plants, 9 pairs of the normal genomic pairs of chromosomes are equal in size, and the tenth pair (XY) consists of one chromosome about the same size as the members of the other pairs, plus one much larger sex chromosome. Heteromorphic pairs of chromosomes have been observed in monoecious strains of cannabis. (14, 15)

K. Hirata concluded that (x) has a higher male tendency than (X), and that (y) has a higher female tendency than (Y). The (X) has a net female tendency, and (Y) has a net male tendency. The male tendency in (Y) overbalances the female tendency in (X) so that a heterogeneous (XY) male is normally male, and a (XX) plant is normally female. Female hemp genes are (XX), (XXX), and (XXXX). The (XXXY) and (XXY) individuals are female or female intersexes. The males are (XY), (XYY), and (XXYY).

S. Hennick, et al., and others assert that this classification is impractical for purposes of breeding hemp, and have developed a new classification based on the theories of Grishko, Neuer, and Migal. The sex of dioecious hemp is determined by two tightly linked genes, both with two alleles. The Y chromosome carries the male allele M and the allele l, which expresses loose inflorescence. The X chromosome carries the female allele F and the allele i (compact inflorescence). Alleles M and l dominate over F and i. A recessive third allele, with a frequency from 0.5-1%, probably exists for monoecious hemp. The sex type of monoecious hemp is determined by autosomes. The sex chromosomes of diploid cannabis carry the genotype liMF and iiFF. The theory, however, does not explain how the loose or compact types of inflorescence are determined in monoecious hemp.(16)

N.D. Migal (All-Union Res. Inst. Fiber Crops, Glukhov) studied the genotypical determination of the sex of hemp. They summarized their finding as follows:

"Monoecious and dioecious hemp plants differ from one another in many  phenotypical characters. As a result, a great variety of sex types is formed, which, in some way, complicates their classification...

 "While studying spontaneous sexual mutations of dioecious and monoecious hemp, some peculiarities of interaction of genetic factors of sex chromosomes and autosomes were found out. They were used in further development of the theory of genotypical sex determination in this plant... The polyfunctional nature of sex determinations connected with monoecious hemp are conditioned by interactions of gene alleles of sexual chromosomes and genetical sexual factor in autosomes of different valency...

"Chromosomal mechanism of sex determination in dioecious hemp plants does not often correspond to expected correlation of the sex types 1:1. This fact, in some way, connected with sex gene mutation in sexual chromosomes and their interaction with autosomal factors." (17, 18)

Table 4.1 ~ Cannabis Genotypes

The Sengbusch Classification system defines five degrees of monoecious forms: (1) 80-90% male flowers; (2) 60-70% male flowers; (3) 40-50% male flowers; (4) 10-30% male flowers; (5) less than 10% male flowers. The second and third degrees types are considered ideal for monoecious cultivation.

The methods developed by R. von Sengbusch and H. Neuer (1943) are the foundation of the breeding technology for monoecious hemp:

"Several trial fields were established in an effort to breed monoecious hemp in a region where no hemp is cultivated. In these fields the progeny of four strains which contain a great number of monoecious plants are cultivated. One field was devoted to plants with many male flowers and only a few female flowers; the second field, to plants with an equal number of male and female flowers.

"Investigation of the distribution of the different types of intersexuality among the progeny of these plants showed that among the progeny of the plants from the first trial field there was an increased number of plants with few female and many male flowers, while in the second field the number of plants with equal number of male and female flowers was increased. This would seem to indicate that selection for different types of intersexuality is possible. While the number of pure male plants in the first year was 10-20%, after repetition of this selection, the number of males decreased to 0.8%, indicating that the male plants have arisen by pollination with pollen of a normal dioecious plant. This result shows that it is necessary to breed and to augment the monoecious hemp in a region where no dioecious hemp varieties are cultivated.

"In the trial field II the number of normal female plants was somewhat increased (11.9%), while in the trial plot I a large number of pure male flowering plants with a female habit (25.5%) appeared, demonstrating that it is impossible to breed from plants with few female and many male flowers a non-segregating variety, and that therefore it is necessary to eliminate these plants in the breeding field before blossoming.

"Trial plot I included, besides the monoecious plants, female plants of a dioecious variety. In the trial plot II there appeared, besides the monoecious plants with the same number of male and female flowers, dioecious plants which practically were females and had only a few male flowers; female plants which arose from monoecious plants, and normal females from a dioecious variety. The progeny from the crosses between these different types were analyzed. The cross of normal females with dioecious plants yielded female plants almost exclusively. This shows that the monoecious plants have the genetic constitution xx, and that dioeciousness is dominant over monoeciousness. This dominance, however, is incomplete; in crosses between pure monoecious plants a small number of female plants arose. The monoecious plants with a very small number of male flowers in crosses with monoecious plants with an equal number of male and female flowers gave about 80% monoecious plants and only 17% female plants. The plants with the same number of female and of male flowers gave, in crosses with the same type of dioecious plants, a small percentage of females, a large percentage of monoecious plants, and a very few male flowering plants. The monoecious plants with a great number of male and a small number of female plants, crossed with the same type of monoecious plants, gave practically no female plants in their progeny, but the greatest number of male flowering plants with female habit. Because these male flowering plants with a female habit have arisen from crosses between two monoecious plants, they must also be xx plants.

"The investigation of descendants of single plants shows great variability in their composition as to sexual types; similar differences could be found between the different strains. The authors explain these observations by the hypothesis that the series of monoecious plants, beginning with the pure female and finishing with male flowering plants with female habit, involve a series of alleles of sex-realisators. The pure female plant xx has the sex-realizator F50 (XX F50F50). The sum is 100 and effects a complete suppression of male flowers. With decrease of the realisator sum the male character of the infloresence increases.

"The male flowering plants with female habit (XX F25 F25 ) have the same sum as the normal male plants (XY F50f)=50. The greater realisator value is almost wholly dominant over the smaller. This explains why in crosses between female and monoecious plants only female plants arise in the F1. The incomplete dominance of the greater realisator value also explains why in crosses between monoecious plants 5-15% female plants always arise. The number of monoecious plants with equal number of male and female flowers which produce monoecious plants is very different among single strains. For breeding therefore it is necesssary to select strains which produce a great number of 'ideal' monoecious plants.

"Two methods for this selection are described. In one the seeds are ascertained in the trial field and in the next year only these strains are cultivated together, and only the seeds from these plants are used. The other method produces results more rapidly. From all strains, those with the greatest number of 'ideal' monoecious plants are established and from these strains the ten best monoecious plants are selected. All other plants are eliminated and the selected plants are cut back. After this treatment the plants begin to sprout and flower again and produce seeds, all of which are derived from selected plants." (35, 36)

The research of W. Hoffmann cast doubt on the theory of realisator-genes:

"Several complimentary genes in the autosome influence the sexual habit of the plant. In the normal dioecious hemp the polymeric habit factors are also influenced by the XY mechanism, so that the male flowers are always combined with the male growth habit, and female flowers with the female growth habit. In the feminized and masculinized types this balance is disturbed and XY types with female growth habit and XX types with male growth habit arise. Because a continuous series exists of feminized forms with many to few male and female flowers and of masculinized forms with many to few female and and male flowers, it would seem that the genes for growth habit can also influence flower formation. The existence of different sex types in segregation proves that the genes for growth habit can also influence flower formation. The existence of different sex types in in segregation proves that the masculinization and the feminization genes are not alleles but independent genes. In the normal dioecious hemp plant, the XY mechanism assures the predominance of one factor over the others. In the intermediate forms of hemp the sum of the efficiency of the genes of the autosomes predominates so greatly that the XY mechanism is not decisive and on the lowest grade the growth habit, on further increase of the efficiency of these genes, also affects flower formation. On the assumption that both dominant and recessive genes are effective as masculinizing and feminizing genes, the large number of sexual and morphological segregates is readily explained."

4.6 ~ Polyploidy

Cannabis usually is a simple diploid plant, but polyploids having several sets of chromosomes can be produced by mutation. Polyploid cannabis usually is larger, produces more resin, and reproduces better than diploids. It is distinguishable by its darker, thicker foliage, and by microscopic analysis. Tetraploid monoecious hemp plants are selected by examination of the number and size of stomata, the number of epidermis and stoma cells, the size of pollen grains, and their number of pores. (19)

Polyploids are valuable for their genetic diversity, but they are unpredictable and usually are unstable in the first generation. They also tend to be sterile and must be propagated by clonal cuttings to be useful for subsequent breeding.

Studies by Warmke and Zhatov revealed that the normal sex ratio for diploids (2n) is nearly 1:1, but tetraploids (4n) form a new class (XXXY) and develop about 7.5 females:1 male, plus female-hermaphrodites. The XXXX is female; XXXY is female-hermaphroditic; XYYY is male-hermaphroditic, and YYYY is male. The XY determination of sex does not account, however, for the development of some monoecious strains. Seemingly, the sexual expression of hemp can be controlled by some other gene set(s) influencing different aspects of flowering. Environmental conditions also can overpower the genetic expression of Cannabis' gender, especially in the final stages of flower production. (20-23)

A. Zhatov (1979) reported these results of his research into hemp genetics:

"Change of ploidy... induced changes on some economically valuable characteristics and biological features. Tetraploid plants of dioecious hemp are characterized with sharply pronounced dioecism: plants with sexual deviations appear in the population of tetraploid hemp. Sex chromosomes of hemp on the tetraploid level play a paramount part in sex determination, but the process of determination is affected by autosomic genes...

"The viability of microspores of polyploid hemp is lower as compared with microspores of diploid hemp. During the storage, polyploid pollen loses the ability to produce pollen tubes of normal length. Selection of plants with the best regulated meiosis may raise the viability of polyploid microspores." (24, 25)

A. Zhatov, N. Migal, and other researchers have used gamma-irradiation of hempseed to mutate the subsequent plant. Presowing irradiation causes a drastic decrease in the survival rate of dioecious male plants and monoecious heterozygotic plants. Male sterility is manifested by empty pollen grains. The proportion of male plants in M1 is reduced to about 14%, and the height of plants is reduced by almost 75%. The number of branches and seed yields are increased, and the fiber content is increased by 30%. (26)

W. Hoffman and E. Knapp treated hemp seeds with x-rays, with these results:

"With increased dosage, the damage to the plants increased, the number of survivors decreased, and the sex ratio changed in favor of the females... With increased dosage, an increasing number of divergent types arose, especially of monoecious plants, and of male-like females. With increased dosage of x-rays, an increased percentage of tendrilled plants was also found... It is possible by means of x-ray treatment to change the sexuality of hemp and to get the normal dioecious hemp to a constant monoecious strain."

When hemp pollen is treated with ultraviolet light for one hour, the seed obtained from the resulting plants produces twice as many females as males.

Colchicine--- Tetraploidy can be induced by the mutagenic alkaloid colchicine, which is found in the autumn crocus, (colchicum autumnale). Colchicine allows a cell to double its chromosomes, but prevents meiosis (the splitting of cells), thus forcing the cells to become polyploid. When applied to cannabis, colchicine produces tetraploid plants which tend to be taller, with greater stem diameter, seed and pollen size. The THC content can increase up to 250%.(27)

A. Zhatov, et al., reported these findings from their research:

"The greatest % of polyploid plants is obtained when hemp plants are treated with 0.5% colchicine solution for 2 hours in the phase of cotyledon leaves. The treatment with colchicine solution inhibits growth. This inhibition continues for 2.5-3 weeks, after which the surviving plants resume normal growth and development. The guard cells in the leaves and the pollen grains of tetraploid plants are larger and the number of pores on the pollen grains are greater. Tetraploid plants are taller and the diameter of their stems, seed size and weight of 1000 seeds are greater. The anatomical structure of the stems differs from the diploid plants in a greater amount of primary and secondary fiber. The pollen viability of the tetraploid plants is lower than that of diploid plants. Vegetation period in tetraploids continues 8-15 days longer than in control plants." (28)

Colchicine also can sprayed on the seeds while they are developing on the mother plant. The flowers of plants treated in this manner should not be smoked because the concentration of colchicine may be dangerously high. A third method is to soak seeds in the solution for 2 to 4 hours. Colchicine stimulates the development of the taproot at first, but this effect ceases within a week; then the seedlings go into shock. About 30% of the survivors will be polyploid.

Colchicine can be bought, or prepared by grinding 100 grams of colchicum seeds to powder and percolating with 2 volumes of ethanol and 1 volume of water. The solution contains approximately 4 milligrams of colchicine. Label the bottle and store it safely: colchicine is toxic. Always wear rubber gloves when handling colchicine.

4.7 ~ Breeding

The great American horticulturist Luther Burbank (1849-1926) bred cannabis and suggested that other plant developers make further explorations of its possibilities. He also described his technique for breeding giant hemp:

"The hemp plant... is cultivated in this country exclusively for the fiber, its seed being almost altogether neglected. Yet the seed of this plant is prized in other countries for its oil, and its neglect here illustrates the same principle of wasteful use of our agricultural resources...

"My experiments with the hemp... have grown out of a suggestion that I made a number of years ago to a large Boston paper manufacturer, to the effect that... hemp might be used as a substitute for wood pulp in the manufacture of paper.

"The experimental work is only at its beginnings, but it seems to be of considerable promise... The hemp, as is well known, is a dioecious plant, and it may be well to mention the simple but uncommon method of making crosses. All the varieties are first planted separately; and only a few of the largest and tallest male and female plants of each variety are left to bloom. When the heads blossom, the tallest of each variety obtained from different sources are crossed with pollen of the tallest male plants.

"After two seasons of this selection and crossing of different strains from different countries, the varieties were combined by crossing, as before, by selecting the largest and tallest plants, out of which a new race was produced of giant hemp...

"Paper made from the fiber of the hemp is found not generally used heretofore, and must certainly be more prized as other pulps become scarce.

"I mention this line of investigation here merely to suggest the wide range of opportunities what will open up for the plant developer when he has learned to cooperate with workers in other industries.

"Hitherto we have been prone to take it for granted that all the valuable textile plants have been investigated and perfected. The newer studies suggest that there is still almost boundless opportunity for progress, not only through the improvement of the plants that have been utilized, but also through the introduction of species that have been ignored or neglected." (29)

In an interview with the Journal of the International Hemp Association (October 1994), the eminent Prof. Dr. Ivan Bocsa (breeder of Kompolti hemp, which gives the highest yield of fiber in the world) explained that he has bred only dioecious and unisex hybrids because self-pollinated inbreeding of monoecious hemp produces about 20% lower stem yield than dioecious varieties:

"The natural state in which hemp appears was and is dioecious. Monoeciousness is artificial in hemp, and it can only exist with the help of man, and without selection, the dioecious state will return in two or three generations. It is therefore very hard and demanding to keep 90 to 95% monoeciousness during seed multiplications. Apart from that, however, monoecious hemp is appropriate only when the crop is grown for so-called double use, i.e., when both stem and seed are harvested... In a dioecious crop, the male plants will be strongly deteriorated when the crop is harvested at seed ripeness, so in this case one needs monoecious cultivars. In Hungary... this double use is unknown. Here fibre hemp is grown as a dense crop which is harvested at the time of male flowering (‘green hemp’), while the seed production takes place in crops grown at a low plant density and with completely different growing techniques...

"Furthermore, monoeciousness has two large disadvantages. In the first place... we have established that 20-25% of self-pollination takes place in monoecious hemp, and this is the cause of... [10-20%] lower stem yield. In the second place, in monoecious hemp, the genetic progress for fibre content is slow, because the so-called Bredemann principle cannot be used. The Bredemann principle consists of the rapid determination of fibre content in male plants before they flower, so that only the males with the highest fibre content are allowed to pollinate the female plants... In monoecious hemp this approach cannot be used, so the rate of genetic progress is only 50% or less of that in dioecious hemp. In spite of these disadvantages, we use a monoecious hemp cultivar in breeding, but only as a parent for unisexual hemp." (30)

The Bredemann Principle for the estimation of fiber content is practiced as follows:

"According to the recommended method, just before budding commences, the stalks of hundreds of male plants are vertically cut in half and the bark is stripped off. The stems are boiled for 3/4 hour in 1.5% NaOH solution, to soften the woody matter. The latter is removed mechanically, care being exercised to avoid loss of fiber. The fibrous mass is then boiled again with dilute NaOH solution, washed, dried and weighed. The woody matter may be weighed or detected by difference. As the resulting fibers are purified more than those of commerce, the weight of hemp so found should be multiplied by 1.25 before computing percentages." (31)

The testing must be performed within a narrow window of only a few days, because the plants will quickly proceed to the flowering stage. Only those males with a high fiber content are allowed to flower; the others are culled. The Bredemann method thus enables breeders to increase the fiber yield of dioecious hemp to 35% within a few generations.

The fiber content of stems is determined by sampling numerous plants from a zone situated between points 30-40% up the stem. In practice, find the middle of the stem and cut from that point downward 15%. After retting or mechanical decortication, the correlative standard of the fiber content is calculated from two weighings of the dry weight of the bark divided by the dry weight of the stem. (32)

The production index of bark fiber content makes it possible to calculate the amount of bark per unit of stem surface, and to discover which parents are productive of dry matter and rich in fiber. The index is derived from the ratio of dry weight of bark to the surface of stem (obtained from the product of height times the median diameter).

H. Neuer, R. von Sengbusch, and H. Prieger developed a rapid method of analysis to select plants for high yield of long fibers and seed:

"The stems are cut into 2 or 3 pieces, and 100 such pieces are put in special frames in which the stems of each individual plant are isolated. In these frames the stems are boiled in 0.25% NaOH for 30 minutes. The bast is removed and put in sieve-boxes which are shaken by machine for 1 hour in 2% NaOH with an addition of Persil. The individual fibers are isolated by the shaking and the perenchymous tissue is pulverized. After shaking, the fibers are washed, dried and weighed. The values so obtained are somewhat too high. For the selection of the different stem weights the fiber content classes are detected by investigating 10 plants. For each weight class the mean fiber content is ascertained and only those plants selected whose fiber content is above the mean of the corresponding weight class. Furthermore, the quantity of fibers is recorded in relation to the surface of the stem. A correlation table for fiber weight to surface of stem is made and all plants with high fiber content are examined with the aid of this second table to eliminate plants with low percentage of wood.

"In the course of the investigation this method was further developed. In order to find plants with many fibers, plants with high bast content must be selected: the stems are cooked for 30 minutes in 0.25% NaOH, and the bast is removed, washed, dried and weighed. The plants with high bast content are investigated as to fiber content to eliminate plants with high bast but low fiber content. The bast is cooked in 2% NaOH for 3 hours, washed, dried and weighed. By this method it is possible to investigate in the same time twice as many plants as by the first method.

"Comparative investigations with the different methods proved that generally high bast content corresponds to high fiber content, but that individual plants with high bast content may have few fibers. These two methods do not make it possible to investigate a very great number of plants; von Sengbusch therefore developed a microscopic method for the examination of the bast- and fiber-structure; stem cutting 3-4 cm long are put in water for 5 minutes until the bast is thoroughly soaked. The cutting then is intensively lighted, but the upper part is darkened. By this manner of illumination the parenchymous tissue remains dark, while the fiber cells show clearly. The stems are investigated by binocular microscope (50x). Plants with a thick bast layer containing many fibers are selected and investigated, by the previously described methods, as to bast- and fiber-content. Only the plants with the highest fiber content are propagated.

"For cross-pollinating hemp the breeding system is the same as that devised by Laube for rye: the seed of each selected plant is divided. In the first year, one half is sown as A-strains and tested as to quality. From the best A-strains, the remainder of the seed is sown the following years as A-strains. In the same way the B-strains are obtained and the strains with lower fiber content are eliminated. The B-strains are used for the production of material for new selection and for the production of super-elite, and elite plants and improved seed." (33)

Prof. Dr. Bocsa developed a unisex cultivar in the 1960s after hempseed for sowing became scarce:

"From the research conducted by McPhee, von Sengbusch and Hoffman we know that when a monoecious hemp plant pollinates a dioecious female the offspring (F1) consists of over 90% of females, or 3-5% of monoecious plants bearing mainly female flowers and only 3-4% of true males. This small number of males however is sufficient to ensure adequate pollination of the crop. As the stand consists mainly of seed-bearing (female and dioecious) plants, with the same habit, we called it unisexual hemp. Such a stand yields 60-80% more seeds than a dioecious cultivar. The seed produced on this stand (F2) is used as sowing seed for fibre production. We called this cultivar Uniko-B. It is, in fact, a 'single cross' between Kompolti and Fibromon, but it is the F2 generation which is commercialized. Von Sengbusch and Hoffman described the phenomenon, but they did not think of its practical use... we make the cross between Kompolti and Fibromon on a surface of 5 hectares; this yields 2500 kg of F1 seed. The F1 seed is sown on a surface of 500 hectares, yielding 400,000 kg of F2 seed, which is used to sow 3,000-3,500 hectares of fibre hemp.

"Unisexuality also can be used to exploit the effect of heterosis [hybrid vigor] which occurs when Chinese and European (Kompolti) cultivars are crossed. This heterosis can increase stem yield by 8-15%. to be able to cross two cultivars we have to construct a female parent which is 'male sterile'. A unisexual F1 can be used as such. In order to obtain a unisexual Chinese line we used Fibrimon as the donor, which was backcrossed many times until we obtained a monoecious line with a Chinese habit. We crossed this line with the original dioecious Chinese cultivar to obtain a unisexual Chinese F1... [with] an unsurpassed seed yield potential of up to 1,500-1,600 kg per hectare...

"In some of my cultivars, bark content is 38-40%; this corresponds to a bast fibre content of 32-34%. If the bark content is higher than 40% the crop may lodge...

"Fibre quality is negatively related to fibre content. As we continue to select for fibre content, we unwillingly increase the proportion of secondary fibre, which has a negative effect on fibre quality."

The fiber content of monoecious cultivars can be increased by 60-100%, up to triple the content of the parent stock, with a content of 30% or more of cleaned fibers.

Monoecious (intersex) varieties of hemp are capable of self-pollinating, which soon leads to inbreeding and depression of desired traits. The cultivation of monoecious hemp is feasible only where hemp is cultivated for both fiber and seeds, to be harvested simultaneously. The strains are not stable and so must be maintained by human intervention.

V.P. Soroka studied the formation of male reproductive system in monoecious and dioecious hemp, and reported that the differences between them at very stage of growth prove that dioecious hemp is biologically superior. (34)

Z. Loseva reported these findings:

"The degree of the manifestation and change in monoecism depends on the growing conditions. When hemp is isolated from other varieties (1.5-2 km) and when the strains are carefully separated at the right times, monoecious hemp preserves 80-90% of the monoecious plants and 0.5-1.5% of the common staminate hemp for many years. If monoecious hemp is grown along with dioecious varieties, monoecism disappears. After two years of growing under such conditions, the monoecious hemp actually becomes converted into dioecious hemp." (37)

The French strains of industrial hemp are "pseudohybrid unisexual" cultivars which are more easily produced and reliably maintained than monoecious varieties:

Parent Stock:    (Dioecious) x (Monoecious) = F1 Generation: (Unisexual) x (Monoecious) = F2 Generation: Marketable Seeds. Dioecious cultivars are bred as follows: Parent Stock: (Dioecious Female) x (Monoecious Male) = F1 Generation: (Female 1) x (Monoecious male) = F2 Generation: (Female 2) x (Monoecious Male) = F3 Generation: (Stable Dioecious Cultivar).

Male plants with insufficient fiber content are removed from the crop before they pollinate; thus, the females are fertilized by the best males only. The seeds of females with the best fiber content are sown the next spring. The selection process is repeated annually.

G.S. Stepanov reported on characteristics of heterosis in unisexual hemp hybrids  which he obtained by crossing maternal dioecious hemp with the paternal monoecious form:

"The F1 generation consisted almost completely of female plants (88.3-98%). Heterosis was established for seed yield, which represents a complex expression of many interrelated reproductive qualities. A discrete character of heterosis for elements of productivity is suggested, based on the height and weight of stem, weight of seeds and weight of fiber." (38, 39)

In a report on the "Phenonemon of unisexuality and heterosis in first generation hemp hybrids", Stepanov declared:

"Intervarietal hybridization of dioecious forms with monoecious forms is a highly effective means for increasing the yield of hemp. The unisexual hybrids are promising for use under commercial conditions, since they can be harvested without hand-picking of staminate hemp, and they have a high yield of stems, seeds and  fiber. Depending on the combination, heterosis can be noted either only for individual elements of the structure or for an entire complex of characters...

"The F1 unisexual hybrids of hemp obtained from crossing dioecious and monoecious varieties most often manifest heterosis in seed yield. The hybrid plants (as compared to the parental forms) are characterized by a higher homeostasis of development... Heterosis has a discrete nature in relation to elements of productivity."

In his "Evaluation of hybridization capacity of hemp cultivars in breeding for heterosis", Stepanov reported:

"Common and specific capacities for hybridization in hemp cultivars are slightly different genetically. Specific capacity for hybridization of the crossing components is of the greatest significance for heterosis manifestation in the first generation hybrids. To obtain a high heterosis effect it is necessary to choose for breeding in the first turn the cultivars with high specific capacity for hybridization...

"When crossing varieties that are equal in height, the variation scope in hemp varietal hybrids exceeds the limits of the ranged series of the parental forms. The highest heritability index (0.79-0.87) is obtained in simple and complex hybrids. To create heterosis hybrids both parents should be selected out of the tall-stalked varieties." (40, 41)

Breeding techniques can be used to stabilize a seed line, to incorporate a desirable trait, or to remove an undesirable charcteristic. The simple process of "line breeding" serves well to maintain the stability of a seed line. Select at least several female plants for seed production, and pollinate only a few of their flowers. If the variety is very inbred, it is advisable to collect pollen from several male plants in order to preserve any diversity in the seedline. Thus, the line can be stabilized for several more generations.

The method of "back-crossing" can be used to stabilize new hybrid seedlines, but it takes several generations to do so. As the name implies, seeds from an earlier generation are crossed with those of later crosses. A second generation (F2) hybrid female is crossed with an F2 male to produce the F3 seed. The F2 and F3 seeds are planted and a worthy F2 female is crossed with a choice F3 male. A male is selected from each subsequent generation (F4, F5, etc.) to be backcrossed with a female grown from F2 seed.

Stepanov reported on the "Variability and heritability of principal elements of productivity in intercultivar hemp hybrids" in 1977:

"The significant effect of backcrosses of paternal forms on the degree of the determination of characters in hemp hybrids was studied. Maternal forms have such an effect for simple and complex intervarietal hybrids. The highest phenotypical variability obtained was connected with the number and weight of seeds per plant. The effect of genotype on the phenotypical manifestation of symptoms is evidently a result of simple and complex intervarietal crosses, so it is easier to make the selection of populations of such hybrids than in back population because environmental conditions insignificantly hide hereditary differences among plants." (42)

In 1978, however, Stepanov reported on "The ineffectiveness of the back-crossing method selection of hemp for heterosis":

"In back crossings the additive effect of the genes predominates. The selection of the characters controlled by the additive genes leads to the homozygous increase of  the population and reduced vitality of the plants. The repeated crossings of the heterozygous hybrid plants with the parental form homozygous for the recessive gene increases the quota of the genes of the latter. It results in the intermediate type of inheritance for all the elements of the backcross hybrid productivity...

"The use of the inbreeding method in hemp breeding... as a method of differentiating a heterogenous population and selection of the most valuable biotypes is the first stage in the creation of controlled heterosis. The investigated hemp cultivars were heterozygotic not only for numerous characters but also for combining ability, which even after 5-fold self-pollination was manifested in different families to a different degree. The magnitude of combining ability of the line was higher, the more strongly it was differentiated genotypically relative to all other lines. In the first stages of practical breeding, the inbreeding methods can be used in creating heterotic variety-line hybrids.

"Heritability of main productivity elements and their anticipated gain in populations of various types of intervarietal hemp hybrids...  plant height and fiber content in a stem, are highly-heritable irrespective of the crossing types. Low heritability is typical of such integral characters, as the number and weight of seeds from one plant; they are modified depending on the growth conditions. The higher the heritability coefficient, the greater the genetic gain of characters. Other conditions being equal, selection is more efficient. From the theoretical view point the expected gain of all the productivity elements at simple and complex intervarietal crossing is considerably higher than at reciprocal ones." (43-45)

M.A. Fedin reported concerning "The efficacy of gametocides inducing male sterility" in 1984:

"The heterotic breeding method is more effective than the methods used before. The breeding process is shorter. It is possible to produce the necessary quantity of hybrid seeds in a shorter period." (46)

K. Goncharova and N. Migal observed "Deviations in meiosis in four sources of hemp male sterility":

"Microsporocytes dying off, migration of the chromosomes beyond the borders of the spindle division in the metaphase and anaphase, lagging chromosomes in the anaphase, formation of the micronuclei in the telophase, and asynchronous division of the microsporocytes." (47)

N.D. Migal also studied the inheritance of the length of the vegetative period:

"Families with different intervals between ripening of male and female plants were revealed in dioecious hemp. This permits breeding for simultaneously ripening forms by selecting families with a minimum interval." (48)

Migal's research also revealed another useful finding:

"The dwarfs of monoecious hemp represent a recessive mutation form valuable for studying peculiarities of natural mutagenesis and changes in the development of sex expression." (49)

The intersexual form of male sterility in the plants of monoecious hemp is characterized by a complete lack of pollen. It is inherited by the next posterity through the monofactorial type of inheritance, which makes it possible to use it as a maternal form in the process of hybridization.

The transition of male to female flowers can be accomplished by wounding the infloresences of male plants. The anther lobes will transform into ovules. The earlier this process begins, the more normal is the development of female flowers. Bisexual flowers also are obtained. (50)

R. Savelli and N. Soster reported the induction of monophylly by wounding hemp:

"[Wounds were inflicted by] extirpation of the apex of the principal bud, cutting of lateral branches, cutting back the plant at various heights, and in all cases total exfoliation... High mortality resulted. The best cases of monophylly occurred in plants cut back 20-25 cm from the ground. Lateral buds grew rapidly in place of the terminals removed. Monophylly is homologized with a juvenile form. The wounding was ineffective in changing the sex ratio."

Monoecy of hemp also can be induced by control of soil moisture. Z. Loseva grew hemp in different watering regimes, with these results:

"Soil moisture of 60-80% proved most suitable for the establishment of monoecy. The seed yield increased with the increased soil moisture. In order to obtain a more widespread monoecy and higher seed yields, hemp should be grown on fertile low-lying fields...

"When the monoecious variety is grown during a shorter day, a smaller number of monoecious plants and lower seed yields are obtained. On the other hand, lengthening of the day, improvement of the water regime, and reasonable ratio of NKP favors a rise in the percentage of monoecious plants and an increase in the seed yields." (51, 52)

Loseva and Arinshtein found these conditions to be optimal for monoecious hemp:

"When grown isolated from other hemp varieties and varietal purity maintained, monoecious hemp consists of 98-99% of monoecious and simultaneously ripening plants. If pure seed is not used, next year the percentage of common fimble will increase 4-6% and a year later to 8-12%. Monoecious hemp cannot be grown on seed plants without isolation or alongside dioecious varieties. The greatest number of monoecious hemp plants was observed under natural day length (79-90%); the smallest, under a short day (32-63%). Consequently the transfer of monoecious hemp varieties into shorter day conditions results in a reduction of seed yield, owing to the decrease in monoecious plants. Optimal conditions for monoecy development are attained by complete mineral fertilizer replacement and by soil moisture equal to 69-80% of the total moisture capacity." (53)

4.8 ~ Light

Cannabis' rate of growth is proportional to the intensity of the light it receives, and is inversely proportional to the length of the photoperiod.

Cannabis responds to light in accordance with the intensity, wavelength, and photoperiod. Cannabis is a "short-day" species: it flowers when the photoperiod decreases to about 8 hours. The plant requires at least 3 hours of light daily just to survive, and at least 8 hours daily to thrive. While the plant is young, up to 3 months old, it responds vigorously to increasingly longer periods of light (up to 16 hours). Daily photoperiods of 16 hours or more will cause cannabis to grow indefinitely in a vegetative phase. The plant will grow about 25% faster under 24-hour lighting. Nutrient consumption increases proportionately. (54)

The photoperiod must be shortened to less than 10 hours to induce flowering and complete the growth cycle. Cannabis flowers quickest with a photoperiod of 8 hours. Thus, mature plants will develop flowers within 2 weeks of short-day treatment. Immature plants require up to one month of long nights to induce flowering. A short light period usually will bring cannabis into bloom within a month after emerging from the ground, but of course the plants will be very small. Short photoperiods inhibit the growth of stems and foliage, leaves produce fewer serrations in the margins. Flowering is hastened. The number of serrations correlates well with the degree of lighttime treatment.

Erratic lighting will confuse cannabis. V. Sofinskaya studied the conditioning of hemp with lighttime, and observed the following effects:

"The decrease in day length favored the acceleration of light stage completion but was unfavorable to plant growth. A prolonged short-day treatment resulted in a greater growth delay and in stunted plants, especially when plants were grown under short-day conditions since their emergence. Sharp changes of light conditions during the light stage resulted in various morphological alterations and in the appearance of hemp forms widely differing in habitat. Changes in light conditions during the light stage caused transgression in the normal course of the stadial plant development, resulting in considerable morphological changes of infloresence development as well as in the shape and size of leaves." (55)

Cannabis must not be disturbed during its night; unscheduled illumination during the dark period will inhibit flowering. Total darkness is required. The flowering response of hemp is controlled by the length of the dark night, not by the length of daylight. As little as 0.03 footcandles (FC) of red light interrupting the dark period will inhibit the anthesis of hemp. A long night thus becomes two short nights separated by an extremely short day, such as 1 minute of illumination.

Very long nights cause hemp flowers to ripen more quickly. This technique is most effective after the 4th week of the flowering phase. Far red light (supplied by incandescent spotlights) can reduce the time required for the flowering phase by about one week.

Cannabis will grow with as little as 800 FC of light, but the growth will not be vigorous. A minimum of 1500 FC is required for a healthy crop. When grown in a short-day regime under low-intensity light, cannabis becomes starved for photons. The hypocotl elongates excessively during the first 2 weeks after the plant emerges. It may reach a height of 6 inches before any internode leaves develop in the plumule. If the illumination is intensified, the plants may survive, and they will develop a clockwise spiral twist in the cotyledon.

Low light levels also produce smaller, thinner leaves, elongated internodes, reduced concentrations of chlorophyll, and less dry weight. High levels of light shorten the growth period, stimulate branching and budding, and increase the production of red anthocyanin pigments. Excessive light causes dessication, bleaching due to photodestruction of chlorophyll, and then necrosis.

Laser light has similar effects. G. Krustev, et al., used a He-Ne laser (632.8 nm/15 & 30 minutes) and a nitrogen laser.  The sowing qualities of the seed are improved, the phases of plant development are shortened, the plants are more vigorous, and the yield of seeds and stems. (83)

Rejuvenation --- The growth cycle of cannabis usually lasts about 16 weeks. When cultivated indoors, however, cannabis can be rejuvenated after it has bloomed and begins to go into senile decline. Some varieties are very amenable to rejuvenation after their flowers have been harvested. The plants should be cut back to the second branching node. Let as many leaves as possible remain, and a few buds. Give the plants at least 18 hours of light daily. New meristems will develop within three weeks. Extra nutrients (especially N) must be supplied at this time, or the new flowers will be male. The process can be augmented with foliar sprays of Indole Acetic Acid (IAA) or Napthalene-AA. The soil should also be treated with the hormones. Hemp can be rejuvenated repeatedly with such treatment, thus living several times longer than usual. Even without continuous-light rejuvenation, female hemp may live several months longer after flowering if the plant remains unpollinated. If female plants become senile between rejuvenations, then sex-reversals usually occur, especially under the influence of short-day photoperiods after the continuous-light treatment. In such a case, about 90% of the females reverse to male or hermaphroditic intergrades. (56-60)

Rejuvenated cannabis blossoms from the terminal bud or from lateral buds below the infloresence. Usually the first few leaves on rejuvenated plants are entire (smooth edged). After several such leaves have developed, subsequent leaves again have the usual serrations. When grown under continuous light, the phyllotaxy of the branches changes from opposite to alternate at some point after the seventh node. Plants grown with normal long-days do not change their phyllotaxy until 12 internodes have developed. Rejuvenated plants are very sensitive to tobacco smoke and can be killed by it.

D. Kohler researched the effects of short and long days on hemp morphology, and found another way to rejuvenate cannabis, based on its response to light:

"In short-day and long-day hemp the first leaves are simple and comparatively broad, the later are divided, their leaflets being comparatively narrow. The size of the leaves following one another is continuously increased. Plants begin to flower (qualitatively reacting short-day hemp in short-day only). The shape of the leaves produced in the infloresence is determined in the first days of flowering: they become more and more simple and their leaflets comparatively broader. The leaf size is influenced by the length of day. The leaves of plants kept in flower-inducing daylength grow less and less due to competition between reproductive and vegetative organs, whilst the leaves of flowering plants, which are transferred into longer day, grow larger and larger. In this case the latest leaves are of the same size and shape as the earliest one; a second life-cycle starts, whilst the plants in the original daylight are dying. Considering the photoperiodic response of hemp, leaf-size is a measure of the physiological age. With monoecious hemp a certain leaf size is necessary for the formation of male flowers. If female plants are put into longer day during blossom, they do imitate the male habit." (61)

Ocra Wilton found a correlation of cambial activity with cannabis' flowering and regeneration:

"A study was made of cross-sections of all the internodes from the tips to the bases of the stems... When Cannabis sativa has reached an advanced stage of reproductiveness, the meristematic tissue of the stem tends to become entirely differentiated into xylem and phloem elements. This anatomical condition is a possible explanation of the death of such plants at the close of one reproductive cycle. The cessation or decline of cambial activity which accompanies the production of flowers in C. sativa progresses from the region of the infloresence toward the base of the plant, which it may or may not reach depending on the degree of reproductiveness which the plant attains. Vigorously vegetative plants have an active cambium throughout their stems... a certain amount of at least potentially meristematic tissue is necessary for a renewal of vegetative growth in stems."

Photoperiodism ---- Photoperiodic control can be very useful to the cannabis breeder. If yield is not important (as is often the case in the early stages of a breeding program), the time required for the life cycle can be greatly reduced by using short photoperiods. Thus, several generations of plants can be produced each year. Under such conditions, cannabis will flower when it is only a few inches tall. (62)

Photoperiodic control makes it possible to synchronize the flowering dates of male and female plants, thus making possible their cross-breeding. Most importantly, photoperiodic control enables breeders to stimulate the production of male flowers on female plants. Self-pollination can be accomplished only by means of such flowers. Male flowers on female hemp do not contain the Y (male) chromosome; they produce only female pollen. When this is used to fertilize female flowers on female plants, they will produce purely female seeds. The pollen from male flowers is of two kinds, and usually produces a ratio of males 1:1 females. A few viable seeds can be obtained from female flowers produced on male plants and self-pollinated, but such seeds are only weakly fertile and produce mostly female plants.

The following procedure will produce seeds which will grow 100% female hemp:

Cultivate two separate groups of female plants indoors. The plants should receive at least 50 watts of light per square foot of growing area. One group must not receive more than 7 hours of light daily. This will induce male flowers to manifest on the female plants. The second group of females must receive about 16 hours of light daily to ensure that no male flowers develop on them. The long photoperiod also inhibits the development of flowers so much that the short-day plants will mature 2 or 3 weeks before the long-day group. Therefore, begin cultivating the long-day females at least 2 weeks before planting the short-day plants.

As the two groups approach maturity, remove any males which may appear. A few weeks before the male hemp begins to flower, the internodes of the stem begin to elongate very quickly. The dominant male enzyme andrase produces thin plants with a tuft of leaves at the top. The leaves are smaller than those of the females, and have fewer leaflets (usually 5). Tiny buds sometimes appear in the nodes about 2/3 up the stalk. The future sexual expression of hemp may be determined by examining these premature flowers. If the buds remain erect, the plant is female. If the buds droop, the plant is male.

When clusters of female buds begin to appear on plants in the long-day group, cover each bud with a transparent plastic bag sealed with a rubber band around the stem below the bud cluster, so as to protect the flowers from accidental pollination.

When male buds appear on some of the female plants in the short-day group, cover each bud with a transparent bag sealed with a rubber band around the stem below the bud cluster, so as to protect the female flowers from accidental pollination.

When male buds appear on some of the females in the short-day group, carefully cut off every male bud and store them in a glass jar. Any new male buds which appear also must be pruned. Within a few days the anthers of the clipped buds will open and release pollen. Collect this pollen and apply it with a thin brush to the stigmas of the bagged flowers in the long-day group. Because this pollen contains only female chromosomes, the fertilized female flowers on the long-day female group will develop seeds which will produce only female plants.(63-66)

Another method of manipulating the gender of cannabis involves treatment of the male pollen with ultra-violet light for about 1 hour. This doubles the ratio of the females to males, perhaps by neutering the weaker male chromosomes. (67, 68)

The viability of hemp pollen can be preserved by the method of Migal and Arinshtein:

Storage of pollen in a refrigerator will protect breeding material for 38-45 days, which is important for crossing different varieties of hemp. Hemp pollen can also be stored in the dark placing it in a desiccator over calcium chloride or concentrated sulfuric acid. Here the pollen grains retain the viability to germinate for 12-18 days. The pollen of dioecious varieties of hemp retain viability longer than the pollen of monoecious varieties. (69)

G. Davidyan found these effects of light on the root development of hemp:

"The growth of the root system in hemp was found to be more intensive than that of the stem at the vernalizaton and light stages. The root system is less vigorous in short than in long day conditions. At the stage of rapid development --- the beginning of budding up to flowering --- an intensive stem and root system growth is observed. The root system of female hemp plants is superior in vigor to that of male plants." (70)

4.9 ~ Sexual Expression

The sexual expression of cannabis is determined by its genetic makeup, and by its metabolic temper, which is regulated by the male enzyme andrase and the female enzyme gynase. Environmental conditions (light, nutrients, soil and water) may suppress the formation of the dominant enzyme, and allow the opposite sex to express itself partially (hermaphroditism) or completely (sex reversal). (71, 72)

E. Galoch found that cytokinin is important for the sexual expession of hemp:

"Transition of female and male hemp plants from the vegetative to the generative phase is associated with a rise in cytokinin level while that of male inflorescences proceeds at a decreasing cytokinin level. The activity of cytokinins apparently is associated with an enhancement of the female tendency..." (73)

Gibberellin will inhibit the formation of flowers on cannabis, but sometimes it will otherwise cause the growth of fertile female flowers on genetically male plants. Silver nitrate or cobalt chloride causes masculinization of flowers of female hemp, possibly due to blockage of ethylene synthesis. High levels of N salts --- and long photoperiods --- have a masculinizing effect on hemp.(74-76)

According to K. Conrad, there are sex-linked differences of the auxin content in male and female hemp plants:

"During blossoming the vegetative parts of the males contain more auxin than those of the females. In the dying leaves and stems a remarkable increase of auxin can be observed." (77)

J. Heslop-Harrison  studied auxin and sexuality in Cannabis:

"Dioecious hemp plants were grown to an age of 20 days in a day-length of 21-22 hours, then given an inductive treatment of ten 8-hour days to initiate flowering. After return to long days and during the period of differentiation of flower buds, a total of 0.5 gr lanolin paste containing 0.5% NapthaleneAcetic Acid (NAA) was applied to leaves at the 3rd and 4th nodes. In genetically male plants, female plants were subsequently formed in sites which would normally be occupied by males, a result which appears to be regulated by the level of native auxin in the vicinity of meristems during the period of differentiation of flower primordia. Secondary effect of auxin treatment were evident in an over-all reduction in intensity of heteroblastic development, the trend towards a reduction of leaf lobing and serration which normally accompanies plants passing through a period of flowering than in untreated controls." (78)

Nitrogen fertilizers masculinize the phenotype by stimulating the formation of male flowers. The proportion, number and degree of monoecious plants increases with increasing N, and the total N content is always higher in monoecious individuals than it is in females. (79)

Treatment of hempseed with ethylene gas will increase the resulting number of female plants by about 50%. Ethylene is produced by certain plants (i.e., bananas, cucumbers and melons), and these can be used to treat hempseed in a simple manner. About two weeks before you plan to sprout the seeds, place them in a paper bag or envelope and put that in a plastic bag with the peels of a ripening banana or cucumber. Replace the peels after a couple of days, and change the bags to prevent mold.

Hempseed can be feminized while they are forming on the plant. Fruit peels are spread around the area for two weeks before the plants enter the flowering phase. Remove the skins when the plants begin to flower. Otherwise, treatment with Etephon will accomplish the same effect.

When hempseed is treated with the female hormone estrogen, percentage of females that are produced will increase by about 10%. Dissolve a birth control pill in water and soak the seeds overnight in the solution. After the initial soaking, continue to treat the seeds by sprouting them on a paper towel soaked in the solution. (80)

A.I. Zhatov tested the effects of ethrel on hemp:

"Treatment of hemp plants with an aqueous solution of ethrel changed the ratio of male to female flowers. The greatest effect was observed when plants were treated during flowering of male flowers." (81)

Electricity also can change the sexual expression of cannabis; B.R. Lazarenko and I.B. Gorbatovskaya reported:

"Under the influence of the electrical current, the numerical proportions between hemp plants of different sexes was changed by comparison with the control to give  an increase of female plants by 20-25%... The characteristics acquired by the plants in electrically treated soils are transmitted by inheritance to the third generation..." [emphasis added] (82)

Photoperiodism is a most useful tool with which to control the sexual expression of cannabis. For example, J. Limberk made a careful study of lighttime on the sexual index of hemp, and reported thus:

"Male plants usually flowered earlier than female. Female plants flowered only when the period of daylight was shorter than 14 hours; male plants flowered even when the day was longer than 14 hours. Reduction of light intensity in the first stages of plant development lead to increases of female plants by 4.3%. Intersexual plants (22-30% of the total) were present in conditions of 11-13 hours light per day. Grafting of plants did not change sex."

Monoeciousness effected by short days  is not fixed in the descendants. (84)

The probable future sex of a pre-floral hemp plant can be guessed at by calculating the Leaf-Mass Index (LMI): Count the points (3, 5, 7) on 3 leaves in the center of a cluster. Divide that number by 3 to determine the average number of points. Repeat the process several times, and figure that average also. Multiply the two averages to determine the LMI. A high LMI indicates that the plant will be female.

The phyllotaxy changes to alternate just before the onset of flowering. Then the sex of the plant can be determined by making a close examination of the upper nodes of the main stem. The onset of flowering is indicated by the appearance of undifferentiated primordial buds behind the stipules at the nodes of the petioles (along the stem at the base of branches). Within a few days they differentiate. The male pistils are flat or knobby with a curved shape and 5 open petals about 5 mm. long; they have a single tiny stalk. Overlapping vegetation often disguises their appearance.

The female develops pairs of flowers surrounded by pointed bracts of protective leaves that will enclose the seed. The female stigma usually appear as 2 fuzzy white hairs forming a "V" that protrudes from a bract. Resinous hairs (glandular trichromes) cover the calyx (2-6 mm long).

4.10 ~ References