Science Fair Project Encyclopedia
- This article is about cannabis as an herb in botany. For other uses, see cannabis.
Cannabis, also known as hemp, is a genus of hardy, dioecious, annual herb. It has been used by humans throughout recorded history for its fiber, for its psychological and physiological potential as a source of drug material, and for the nourishment and oil of its seeds. Different parts of the herb have different uses and different varieties are cultivated in different ways, and harvested at different times, depending on the purpose for which the herb is grown.
The tough fiber of the plant, cultivated as hemp, has numerous textile uses. Its seed, chiefly used as caged-bird feed, is a valuable source of protein, energy, and long-chain fatty acids, and also contain oil that can be used to make paints, varnishes and soaps. Most concentrated in the resin in the buds of the female plant, mildly psychedelic and other psychoactive and physiologically active chemical compounds known as cannabinoids are consumed for recreational, medicinal, and spiritual purposes. When so purposed, preparations of buds and leaves, sometimes called marijuana, and preparations derived from resinous extract, sometimes called hashish, are today usually consumed by inhaling a vapor released by smoking or other heating, or by oral ingestion. Historically, tinctures, teas, and ointments were also common preparations.
Cannabis reproduces sexually. The flowers of the female plant, in cannabis usually called buds, are arranged in racemes and can produce hundreds of seeds. Males reach sexual maturity several weeks prior to females. Although genetics disposes a plant to become male, environmental factors, including the diurnal light cycle, can alter the sex. Natural hermaphrodites, with both male and female parts, are usually sterile but artificially induced hermaphrodites can have fully functional reproductive organs. 'Feminized' seed sold by many commercial seed suppliers are derived from artificially hermaphrodytic females that lack the male gene or by treating the seeds with hormones.
Cannabis uses C4 photosynthesis, which is not dependent upon a night cycle for carbon dioxide absorption. A cannabis plant in the vegetative growth phase of its life cycle can thrive under twenty-four hour daylight conditions, although some growers advocate a small rest period to avoid overstressing the plant. Flowering usually occurs when darkness exceeds eleven hours per day and can take up to six weeks.
In soil, the optimum pH for the plant is 6.5 to 7.2. In hydroponic growing, the nutrient solution is best at 5.2 to 5.8, making cannabis well-suited to hydroponics because this pH range is hostile to most bacteria and fungi.
Broadly, there are three groups of cannabis varieties that are cultivated today:
- Varieties primarily cultivated for their fibre, characterized by long stems and little branching.
- Varieties grown for medicinal or recreational purposes. A nominal if not legal distinction is often made between hemp, with concentrations of psychoactive compounds far too low to be useful for that purpose, and marijuana.
The family Cannabaceae was formerly placed with the nettles in the order Urticales, but is now considered to be in the order Rosales. There is phylogenetic controversy as to whether the cultivated varieties of the plant are of a single species (Cannabis sativa) or represent distinct species (such as those called Cannabis indica, Cannabis ruderalis, or Cannabis americana). That there are different strains of cannabis has not been in question; whether these strains possess qualities of a true species or lesser taxonomic designations, such as races, ecotypes, cultivates, chemovars, and so on, has been at issue (Schultes and Hofmann 1980). Current research indicates the classification consists of more than one species. Botanists such as Richard E. Schultes at Harvard University and Loran C. Anderson at Florida State University conclude sufficient scientific evidence exists to support three species of cannabis: Cannabis sativa, Cannabis indica, and Cannabis ruderalis. C. sativa grows to a height of 18 feet (6 metres), is loosely branched, and thrives in hot, dry climates. C. indica grows from 3.5 to 4 feet (1.3 metres), is conical in shape, and thrives in cool, damp climates. C. ruderalis grows from 1 to 2.5 feet (0.4 to 0.7 m), is dense and never branches, and is found primarily in Russia. There are other distinguishing features as well, related to cell and leaf structures. There are gelatinous fibers in the wood and vessels that exist singly or in small groups in C. sativa. C. indica has liberiform fibers in its wood and its vessels occur in large groups. C. ruderalis is mostly intermediate in these characteristics. Although the number of leaflets may vary within a species, C. sativa normally has seven leaflets, C. indica has nine, and C. ruderalis has three. The leaflet of C. sativa is narrow, or lanceolate. The C. indica leaflet is broad, or oblanceolate. And the C. ruderalis leaflet is oval, or elliptic, being broadest at the mid-length of the leaf (Anderson 1974, 1980). All three species contain THC; C.indica produces the most and C. ruderalis the least. Cannabis has been cultivated for thousands of years for its intoxicating flowering tops and leaves, its fibrous stems and branches, and its nutritious seeds. A strain that is high in one of these three qualities tends to be low in the other two. C. indica, for example, is very low in fiber content but generates the most potent marijuana. C. sativa produces the hemp fibers that have been used for centuries for making rope and coarse woven produces, but races of C. sativa high in this quality contain very little THC (less than 0.5 percent). The seeds of C. sativa can also be harvested for use as animal feed and for producing oil that is used in cooking and in making paint.
Though the main psychoactive chemical compound in cannabis is Delta-9-tetrahydrocannabinol (THC), the plant is known to contain about sixty cannabinoids, including two others of particularly high concentration, cannabinol (CBN) and cannabidiol (CBD). CBD is a precursor to THC, and CBN is a product of the degradation of THC by exposure to oxygen. Differences in the chemical composition of cannabis varieties may produce different effects in humans. Synthetic THC, called dronabinol, does not contain CBD, CBN, or other cannabinoids, which is one reason why its pharmacological effects may differ significantly from those of cannabis preparations.
Most commonly available marijuana contains below 8% THC. Selective breeding and modern cultivation techniques like hydroponics have produced varieties with more than 25% THC (compare to: ). With varieties containing below 2% THC, such as those specifically cultivated for use as hemp, smoking may produce lightheadedness or mild headache but not inebriation. The THC content is also affected by the sex of the plant, with female plants generating substantially more resin than their male counterparts. Seedless varieties derived from unpollinated female plants have high THC content and are traditionally known as sinsemilla (Spanish: "without seed").
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