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Cannabis Botany

The following description of cannabis botany is drawn largely from Rob Clarke's Marijuana Botany. [1]

Cannabis is an annual herb that can grow as tall as 6 meters (about 20 feet) at a rate of up to 7 centimeters (2 inches) per day under optimal conditions. Seeds are planted in the spring and typically germinate in 3 to 7 days. The first two "seed leaves" are small and rounded at the tip. Above the seed leaves, the first true leaves arise, opposite each other. Subsequent leaf sets form opposite each other, each usually having two leaflets more than the previous set, up to as many as 11 leaflets. Five to seven leaflets is typical in the mature plant. After a few weeks the leaf sets switch from an opposite to a staggered formation along the stem which is an indicator that they are mature enough to enter the flowering cycle.

With enough space and light, the intersection where each leaf forms along the main stem becomes the source of a new branch. When cultivated for maximal flower formation, plants are "encouraged", through adjustments in lighting and spacing, to develop as many of these intersections as possible because they later become the source of the flowers.

Light requirements for cannabis vary depending on the phase of growth. During its vegetative phase, which is characterised by vigorous leaf growth, the plant can profitably utilise anywhere from 14 to 24 hours of light. But flower formation generally requires the onset of shorter days, corresponding to fewer than 14 hours of light per day.

In Northern latitudes (where most cannabis has historically been grown) this generally corresponds to the months of August through October.

The specific light requirements of cannabis vary depending on the indigenous conditions associated with each strain, so that an equatorial variety, for example, might need less adjustment in the light cycle to mature fully than a more Northern or Southern variety, which would likely require considerable adjustment. Plants that receive inappropriate light/dark ratios or whose periods of darkness are interrupted, are at increased risk for developing sparsely or malformed flowers.

Individual cannabis plants are either male or female, but examples of plants displaying both sexes (hermaphrodites) are found. The appearance of the flowers varies significantly. While male flowers consist of loosely hanging groups of yellowish pollen pods, female flowers are dense, tight, erect clusters of pistils that start out white and turn red as they mature. In the early phases of flowering, the distinction between males and females is unclear, but usually within two to three weeks, the first female pistils become visible along the nodes of the main stem while the early male flower formations take somewhat longer to show themselves. Cultivators wait until flowers are fairly well formed before they begin to separate the plants, usually culling males in order to produce more potent "sensimillan" (seedless) varieties.

The flowering patterns of male and female plants vary significantly from each other. Female plant characteristics are apparent one to two weeks earlier than in the male, but may take a month longer to go into rapid flower formation. Once flowering begins, female plants continue to increase flower mass for up to 5 months until full maturation. The male plant forms its flowers, releases its pollen, and dies soon thereafter.

Once male pollen makes contact with a female pistil, germination occurs within minutes. The seeds mature within 2 to 5 weeks and generally drop from the plant around this time. They are patterned in grey, brown, or black and generally measure between 2 to 6 millimeters in length and 2 to 4 millimeters in diameter. If desired, pollination can be purposefully limited to a single branch on a plant that can produce hundreds of viable seeds while the remaining branches produce seedless floral clusters.

As the seedless clusters continue to mature, the calyxes swell, and sticky mushroom-shaped glands, known as trichomes, form on the surface secreting aromatic THC-laden resins. THC is the main psychoactive constituent in cannabis and is most concentrated in these glands. Different varieties of cannabis produce varying concentrations of trichomes, and indica strains are believed to be more resinous than sativas, possibly because of the increased light found in the tropical regions from which indicas originate. [2]

References used above
  1. Clarke, Robert Connell. "Marijuana Botany, An Advanced Study: The Propagation and Breeding of Distinctive Cannabis". Ronin Publishing. Berkeley, CA. 1981.
  2. Conrad, Chris. "Hemp for Health". Healing Arts Press. Los Angeles, CA. 1993, 1994, p.22.