高中英语 Unit3 Protecting ourselves文化背景 牛津译林版选修10-牛津版高二选修10英语素材

Unit3 Protecting ourselves 文化背景CannabisCannabis is an annual, dioecious, flowering herb. The leaves are palmately compound, with s errate 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, t his 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.Cannabis normally has imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separ ate plants. It is not unusual, however, for individual plants to bear both male and female flowers. Although monoecious plants are often referred to as "hermaphrodites," true hermaphrodites (which are less common) bear staminate and pistillate structures on individual flowers, whereas monoecious plants bear male and female flowers at different locations on the same plant. Male flowers are normally borne on loose panicles, and female flowers are borne on racemes. All known strains of Cannabis are wind-pollinated and produce "seeds" that are technically called achenes. Most strains of Cannabis 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.Cannabis is naturally diploid, having a chromosome complement of 2n=20, although polyploid individuals have been artificially produced. The plant is believed to have originated in the mountainous regions northwest of the Himalayas. It is also known as hemp, although this term is often used to refer only to varieties of Cannabis cultivated for non-drug use. Cannabis plants produce a group of chemicals called cannabinoids, which produce mental and physical effects when consumed. Cannabinoids, 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 flower buds (marijuana), resin (hashish), or various extracts collectively known as hashish oil. In the early 20th century, it became illegal in most of the world to cultivate or possess Cannabis for drug purposes.