BY ROSENTHALL. GENETICS AND SEX IN CANNABIS Sex is an inherited trait in Cannabis, and can be explained in much the same terms as human sexuality can. Like a human being, Cannabis is a diploid organism: its chromosomes come in pairs. Chromosomes are microscopic structures within the cells on which the genes are aligned. Cannabis has 10 pairs of chromosomes (n=10), for a total of 20 chromosomes (2m=20). One pair of chromosomes carries the primary genes that determine sex. These chromosomes are labelled either X or Y. Male plants have an XY pair of sex chromosomes. Females have XX. Each parent contribute one set of 10 chromosomes, which includes one sex chromosome, to the embryo. The sex chromosome carried by the female ovule can only be X. The one carried by pollen of the male plant may be either X or Y. From the pollen, the embryo has a 50/50 chance of receiving an X, likewise for Y; hance, male and female progeny appear in equal numbers (in humans, the sperm carries either an X or a Y chromosome.) 17.2 Flowering Male Plant Under natural light, males usually start to flower from one to four weeks before the females. Where the photoperiod is artificially controlled, as with electric lights, males respond quickly (in about a week) to a change to short photoperiods and usually show flowers sooner than the females. Male flowers develop quickly, in about one to two weeks on a vigorous plant, not uniformly. Scattered flowers may open a week or more before and after the general flowering, extending the flowering stage to about four weeks. The flowering stage continues to demonstrate the male's tall, relatively sparse growth. Most of the flowers develop near the top of the plant, well above the shorter females. The immature flower buds first appear at the tips of the main stem and branches. Then tiny branches sprout from the leaf axils, bearing smaller clusters of flowers. The immature male flowers are closed, usually green, and develop in tight clusters of knob-like buds. The main parts of the male flowers are five petal-like sepals which enclose the sexual organs. As each flower matures, the sepals open in a radiating pattern to reveal five pendulous anthers (stamens). Inside the ovoid, sac-shaped anthers, pollen grains develop. Initially, pollen sifts through two pores near the top of the anther; then, starting from the pores, longitudinal slits slowly open (zipperlike) over the course of a day, releasing pollen to the wind. Once a flower sheds pollen, it shortly dies and falls from the plant. Normally, male plants begin to die one to two weeks after the bulk of their flowers have shed pollen. Healthy males may continue to flower for several more weeks, but secondary growth seldom has the vigour of initial bloom. Female Plant The female plant generally starts to flower later than the male, under either natural light or an artificially controlled photoperiod. Female marijuana plants flower when the average daily photoperiod is less then about 12 to 13 hours. However, some varieties and individuals may flower with a photoperiod of over 14 hours. Some Colombian varieties may not respond until the photoperiod falls below 12 hours for a period of up to three weeks. The duration of flowering also depends on the particular rhythm of the variety, as well as growing conditions, and whether or not the plant is pollinated. Within these variables, females maintain vigorous growth and continue to rapidly form flowers for a period that ranges from 10 days to about eight weeks. Females generally do not grow much taller during flowering. Growth emphasises a "filling out," as flower clusters develop from each leaf axil and growing tip. Normally, the flowers arise in pairs, but the pairs form tight cluster of 10 to over 100 individual flowers that are interspersed with small leaves. These clusters are the "buds" of commercial marijuana. Along the top of the main stem and vigorous branches, "buds" may form so thickly that the last foot or more of stem is completely covered. Usually the leaves that accompany the flowers tend toward simpler structure, until each leaf has one to three blades. The visible parts of the female flower are two upraised stigmas, one-quarter to one-half inch long, usually white or cream, sometimes tinged with red, that protrude from a tiny, green, pod-shaped structure called the floral bract. This consists of modified leaves (bracts and bracteoles) which envelop the ovule or potential seed. The mature bract is a tiny structure, about 1/8 inch across and 1/4 inch long. When fertilised, a single seed begins to develop within the bract, which then swells until it is split by the mature seed. Bracts are covered more densely with large resin glands than is any other part of the plant, and are the most potent part of the harvest. Resin glands may also be seen on the small leaves that are interspersed among the flowers. The differences between male and female Cannabis become more apparent as the plants mature. The same can be said of the differences between varieties. Often, two varieties may appear to be similar, until they actually flowers and fill out to different forms. These appear in many ways: some varieties maintain opposite phyllotaxy with long internodes throughout flowering; bud sizes vary from about one-half inch to about three inches, with a norm of about one to two inches; buds may be tightly arranged along the stem, yielding a "cola" two feet long and four inches thick; and some varieties only form buds along their main stem and branch tips, with a few "buds" forming along the branches. When a female is well-pollinated, growth slows and the plant's energy goes into forming seeds and thus into the continuation of the species. Some plants (but only the more vigorous ones) will renew flowering even when pollinated. Females that are not well-pollinated continue to form flowers rapidly. This extends the normal flowering period, of 10 days to four weeks, up to eight weeks or more. Individual flowers are pollinated by individual pollen grains. In a matter of minutes from its landing on a stigma, the pollen grain begins to grow a microscopic tube, which penetrates the stigma and reaches the awaiting ovule wrapped within the bracts. The pollen tube is a passageway for the male's genetic contributions to the formation of the embryo (seed). The union of the male and female complements of genes completes fertilisation and initiates seed formation. The stigmas, having served their purpose, shrivel and die, turning rust or brown colour. On a vigorous female, the seeds reach maturity in about 10 days. When growing conditions are poor, the seed may take five weeks to ripen to full size and colour. Naturally, all the flowers do not form, nor are they pollinated at the same time - and there will be seeds that reach maturity weeks before others do. Although each flower must be individually fertilised to produce a seed, a single male plant can release many millions of pollen grains. A large female plant can produce over 10,000 seeds. 17.3 Sexual Variants in Cannabis Cannabis has been studied for many years because of its unusual sexuality. Besides the normal dioecious pattern, where each plant bears exclusively male or female flowers, it is not uncommon for some plants to have both male and female flowers. These are called hermaphrodites, or monoecious plants, or intersexes. Hermaphroditic plants form normal flowers of both sexes in a wide variety of arrangements, in both random and uniform distributions. Natural Hermaphrodites Some hermaphrodites seem to be genetically determined (protogenous). That is, they naturally form flowers of both sexes given normal growing conditions. Possibly genes carried on the autosomes (the chromosomes other than the sex chromosomes) modify the normal sexual expression. Monoecious varieties have been developed by hemp breeders in order to ensure uniform harvests. It is also possible that these particular are polyploid, which means they have more than the usual two sets of chromosomes. This kind of hermaphrodite may have XXY (triploid), or XXYY or XXXY (tetraploid) sex chromosomes. However, no naturally occurring polyploids have ever been verified (by observation of the chromosomes) in any population of Cannabis. Polyploids have been induced in Cannabis by using mutagens, such as the alkaloid colchicine. Whatever then genetic explanation may be, one or more of these natural hermaphrodites may randomly appear in any garden. They are sometimes faster-maturing, have larger leaves, and are larger in overall size than their unisexual siblings. They usually form flowers of both sexes uniformly in time and distribution, and in some unusual patterns. For example, from Mexican seed, we have seen a plant on which separate flowering cluster consisted of both female and male flowers: and upper section of female flowers had upraised stigmas, and a lower section of male flowers dangled beneath the female flowers. In other plants from Mexican seed, the growing tips throughout the plant have female flowers; male flowers sprout from the leaf axils along the main stem and branches. Plants from "Thai" seed sometimes form male and female flowers on separate branches. Branches with female flowers tend to predominate, but branches having mostly male flowers are located throughout the plant. Abnormal Flowers, Intersexes, Reversals Gender is set in the new plant at the time of fertilisation by its inheritance of either the X or the Y chromosome from the male (staminate) plant. With germination of the seed, the environment comes into play. Heritage sets the genetic program, but the environment can influence how the program runs. (Sexual expression in Cannabis is delicately balanced between the two.) The photoperiod, for example, controls the plant's sequence of development. Also, the plant's metabolism and life processes are dependent on growing conditions. When the environment does not allow a balance to be maintained, the normal genetic program may not be followed. This is mirrored by abnormal growth or sexual expression. Abnormal Flowers Abnormal sexual expression includes a whole range of possibilities. Individual flowers may form abnormally, and may contain varying degrees of both male and female flower parts. For instance, a male flower may bear a stigma; or an anther may protrude from the bracts of a female flower. Abnormally formed flowers are not often seen on healthy plants, although if one looks hard enough, a few may be found in most crops. When many of the flowers are abnormal, an improper photoperiod (coupled with poor health) is the most likely cause. Abnormal flowers sometimes form on marijuana grown out of season, such as with winter or spring crops grown under natural light. Intersexes and Reversals Much more common than abnormally formed flowers is for the plant's sex to be confused. One may find an isolated male flower or two; or there may be many clusters of male flowers on an otherwise female plant, or vice versa. These plants are called intersexes (also hermaphrodites or monoecious plants). Intersexes due to environment causes differ from natural hermaphrodite in having random distributions and proportions of male and female flowers. In more extreme cases, a plant may completely reverse sex. For example, a female may flowers normally for several weeks, then put forth new, sparse growth, typical of the male, on which male flowers develop. The complete reversal from male flowering to female flowering also happens. All other things being equal, the potency of intersexes and reversed plants is usually less than that of normal plants. If there are reversals or intersexes, both of the sexes will usually be affected. Female plants that reverse to male flowering show the biggest decline. Not only is the grass less potent, but the amount of marijuana harvested from male flowers is negligible compared to the amount of marijuana that can be harvested from a normal female. Plants that change from male to female flowering usually increase their potency, because of the growth of female flower bracts with their higher concentration of resin. Female flowers on male plants seldom form as thickly or vigorously as on a normal female. Between the loss in potency and the loss in yield because of females changing to males, a crop from such plants is usually inferior, in both yield and potency, to one from normal plants. Environmental Effects Many environmental factors can cause intersexes and sexual reversals. These include photoperiod, low light intensity, applications of ultraviolet light, low temperatures, mutilation or severe pruning, nutrient imbalances or deficiencies, senescence (old age), and applications of various chemicals (see bibliography on sex determination). The photoperiod (or time of planting using natural light) is the most important factor to consider for normal flowering. In 1931, J. Schaffner (105) showed that the percentage of hemp plants that had confused sexual characteristics depended on the time of year they were planted. Normal flowering (less than five percent of the plants are intersexes) occurred when the seeds were sown in May, June, or July, the months when the photoperiod is longest and light intensity is strongest. When planted sooner or later in the year, the percentage of intersexuals increased steadily, until about 90 percent of the plants were intersexual when planted during November or early December. Marijuana plants need more time to develop than hemp plants at latitudes in the United States. Considering potency, size, and normal flowering, the best time to sow for the summer crop is during the month of April. Farmers in the south could start the plants as late as June and still expect fully developed plants. If artificial light is used, the length of the photoperiod can influence sexual expression. Normal flowering, with about equal numbers of male and female plants, seems to occur when the photoperiod is from 15 to 17 hours of light for a period of three to five months. The photoperiod is then shortened to 12 hours to induce flowering. With longer photoperiods, from 18 to 24 hours a day, the ratio of males to females changes, depending on whether flowering is induced earlier or later in the plant's life. When the plants are grown with long photoperiods for six months or more, usually there are at least 10 percent more male then female plants. When flowering is induced within three months of age, more females develop. Actually, the "extra" males or females are reversed plants, but the reversals occur before the plants flower in their natural genders. Some plants will flower normally without a cutting of the photoperiod. But more often, females will not form thick buds unless the light cycle is cut to a period of 12 hours duration. Don't make the light cycle any shorter than 12 hours, unless the females have not shown flowers after three weeks of 12-hour days. Then cut the light cycle to 11 hours. Flowers should appear in about one week. Anytime the light cycle is cut to less than 11 hours, some intersexes or reversed plant usually develop. This fact leads to a procedure for increasing the numbers of female flowers indoors. The crops can be grown for three months under a long photoperiod (18 or more hours of light). The light cycle is then cut to 10 hours. Although the harvest is young (about five months) there will be many more female flower buds than with normal flowering. More plants will develop female flowers initially, and male plants usually reverse to females after a few weeks of flowering. Of the other environmental factors that can affect sexual expression in Cannabis, none are as predictable as the photoperiod. Factors such as nutrients or pruning affect the plant's overall health and metabolism, and can be dealt with by two general thoughts. First, good growing conditions lead to healthy plants and normal flowering: female and male plants occur in about equal numbers, with few (if any) intersexes or reversed plants. Poor growing conditions lead to reduced health and vigour, and oftentimes to confused sex in the adult plant. Second, the age of the plants seems to influence reversals. Male plants often show female flowers when the plant is young (vigorous) during flowering. Females seven or more months old (weaker) often develop male flowers after flowering normally for a few weeks. Anytime the plant's normal growth pattern is disrupted, normal flowering may be affected. For instance, plant propagated from cuttings sometimes reverse sex, as do those grown for more than one season.