Trichomes [trik-ohm] (from the Greek word ‘trikhoma’ meaning ‘growth of hair’) are structures on plants that look like hairs. Glandular trichomes have chemicals in them. They break when the plant is touched. For example, trichomes on poison ivy leaves have a chemical that causes a rash. Cannabis trichomes produce a psychoactive resin. It is likely that in many cases, plant hairs interfere with the feeding of herbivores. Hairs on plants growing in areas subject to frost keep the frost away from the living surface cells. In windy locations, hairs break-up the flow of air across the plant surface, reducing evaporation. Dense coatings of hairs reflect solar radiation, protecting the more delicate tissues underneath in hot, dry, open habitats. And in locations where much of the available moisture comes from cloud drip, hairs appear to enhance this process.

They occur only on plants and certain protists (a type of single-celled organism). Certain algae, have their terminal cell shaped into an elongate ‘hair-like’ structure called a trichome. The same term is applied to such structures in some cyanobacteria (bacterium which rely on photosynthesis). Trichomes on plants are epidermal outgrowths of various kinds. The terms ’emergences,’ ‘thorns,’ ‘spines,’ and ‘prickles’ refer to outgrowths that involve more than the epidermis (the outermost layer of the plant). See for example, the ‘wait-a-minute tree,’ which has numerous hooked thorns with the shape and size of a cat’s claw, that tend to hook onto passers-by; the hooked person must stop (‘wait a minute’) to remove the thorns carefully to avoid injury.

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