<unk>  growing as weeds at the foot of Dhaulagiri, Nepal. A thicket of wild<unk>  in Islamabad, Pakistan.<unk>  is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions. At the top of a flowering plant, this number again diminishes to a single leaflet per leaf. The lower leaf pairs usually occur in an opposite leaf arrangement and the upper leaf pairs in an alternate arrangement on the main stem of a mature plant. The leaves have a peculiar and diagnostic venation pattern that enables persons poorly familiar with the plant to distinguish a<unk>  leaf from unrelated species that have confusingly similar leaves (see illustration). As is common in serrated leaves, each serration has a central vein extending to its tip. However, the serration vein originates from lower down the central vein of the leaflet, typically opposite to the position of, not the first notch down, but the next notch. This means that on its way from the midrib of the leaflet to the point of the serration, the vein serving the tip of the serration passes close by the intervening notch. Sometimes the vein will actually pass tangent to the notch, but often it will pass by at a small distance, and when that happens a spur vein (occasionally a pair of such spur veins) branches off and joins the leaf margin at the deepest point of the notch. This venation pattern varies slightly among varieties, but in general it enables one to tell<unk>  leaves from superficially similar leaves without difficulty and without special equipment. Tiny samples of<unk>  plants also can be identified with precision by microscopic examination of leaf cells and similar features, but that requires special expertise and equipment. Reproduction All known strains of<unk>  are wind-pollinated and the fruit is an achene. Most strains of<unk>  are short day plants, with the possible exception of C. sativa subsp. sativa var. spontanea (= C. ruderalis), which is commonly described as "auto-flowering" and may be day-neutral.<unk>  is predominantly dioecious, having imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separate plants. "At a very early period the Chinese recognized the<unk>  plant as dioecious", and the (c. 3rd century BCE) Erya dictionary defined xi 枲 "male<unk> " and fu 莩 (or ju 苴) "female<unk> ". Male flowers are normally borne on loose panicles, and female flowers are borne on racemes. Many monoecious varieties have also been described, in which individual plants bear both male and female flowers. (Although monoecious plants are often referred to as "hermaphrodites", true hermaphrodites – which are less common in<unk>  – bear staminate and pistillate structures together on individual flowers, whereas monoecious plants bear male and female flowers at different locations on the same plant.) Subdioecy (the occurrence of monoecious individuals and dioecious individuals within the same population) is widespread. Many populations have been described as sexually labile. As a result of intensive selection in cultivation,<unk>  exhibits many sexual phenotypes that can be described in terms of the ratio of female to male flowers occurring in the individual, or typical in the cultivar. Dioecious varieties are preferred for drug production, where the fruits (produced by female flowers) are used. Dioecious varieties are also preferred for textile fiber production, whereas monoecious varieties are preferred for pulp and paper production. It has been suggested that the presence of monoecy can be used to differentiate licit crops of monoecious hemp from illicit drug crops, but sativa strains often produce monoecious individuals, which is possibly as a result of inbreeding.<unk>  female flower with visible trichomes Male<unk>  flower buds Sex determination<unk>  has been described as having one of the most complicated mechanisms of sex determination among the dioecious plants. Many models have been proposed to explain sex determination in<unk> . Based on studies of sex reversal in hemp, it was first reported by K. Hirata in 1924 that an XY sex-determination system is present. At the time, the XY system was the only known system of sex determination. The X:A system was first described in Drosophila spp in 1925. Soon thereafter, Schaffner disputed Hirata's interpretation, and published results from his own studies of sex reversal in hemp, concluding that an X:A system was in use and that furthermore sex was strongly influenced by environmental conditions. Since then, many different types of sex determination systems have been discovered, particularly in plants. Dioecy is relatively uncommon in the plant kingdom, and a very low percentage of dioecious plant species have been determined to use the XY system. In most cases where the XY system is found it is believed to have evolved recently and independently. Since the 1920s, a number of sex determination models have been proposed for<unk> . Ainsworth describes sex determination in the genus as using "an X/autosome dosage type". The question of whether heteromorphic sex chromosomes are indeed present is most conveniently answered if such chromosomes were clearly visible in a karyotype.<unk>  was one of the first plant species to be karyotyped; however, this was in a period when karyotype preparation was primitive by modern standards (see History of Cytogenetics). Heteromorphic sex chromosomes were reported to occur in staminate individuals of dioecious "Kentucky" hemp, but were not found in pistillate individuals of the same variety. Dioecious "Kentucky" hemp was assumed to use an XY mechanism. Heterosomes were not observed in analyzed individuals of monoecious "Kentucky" hemp, nor in an unidentified German cultivar. These varieties were assumed to have sex chromosome composition XX. According to other researchers, no modern karyotype of<unk>  had been published as of 1996. Proponents of the XY system state that Y chromosome is slightly larger than the X, but difficult to differentiate cytologically. More recently, Sakamoto and various co-authors have used RAPD to isolate several genetic marker sequences that they name Male-Associated DNA in<unk>  (MADC), and which they interpret as indirect evidence of a male chromosome. Several other research groups have reported identification of male-associated markers using RAPD and AFLP. Ainsworth commented on these findings, stating, Environmental sex determination is known to occur in a variety of species. Many researchers have suggested that sex in<unk>  is determined or strongly influenced by environmental factors. Ainsworth reviews that treatment with auxin and Ethylene as a plant hormone#ethylene have feminizing effects, and that treatment with cytokinins and gibberellins have masculinizing effects. It has been reported that sex can be reversed in<unk>  using chemical treatment. A PCR-based method for the detection of female-associated DNA polymorphisms by genotyping has been developed. File:Hemp plants-cannabis sativa-single 3.A male hemp plant File:Cannabis indica Selkem.Dense raceme of female flowers typical of drug-type varieties of<unk>  Biochemistry and drugs<unk>  plants produce a group of chemicals called<unk> oids, which induce mental and physical effects when consumed.<unk> oids, terpenoids, and other compounds are secreted by glandular trichomes that occur most abundantly on the floral calyxes and bracts of female plants. As a drug it usually comes in the form of dried infructescences ("buds" or "marijuana"), resin (hashish), or various extracts collectively known as hashish oil. During the 20th century, it became illegal in most of the world to cultivate or possess<unk>  for sale, and even sometimes for personal use. File:Cannabis sativa radix profile.Root system side view File:Cannabis sativa radix topview.Root system top view File:Cannabis hemp sativa (left) indica (right).Micrograph C. sativa (left), C. indica (right) Chromosomes and genome<unk> , like many organisms, is diploid, having a chromosome complement of 2n=20, although polyploid individuals have been artificially produced. The first genome sequence of<unk> , which is estimated to be 820 Mb in size, was published in 2011 by a team of Canadian scientists.
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Heroin
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Phencyclidine
Methamphetamine
Nicotine