Epidermis-5

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Epidermis-5
		Trichomes are usually divided into four categories, single cell or multiple, secretory or nonsecretory. This is the stinging hair of Urtica (Stinging Nettle) is a single cell, secretory trichome. The tip has a weak spot that is easily broken by contact. Note that the base is swollen like a sprayer bulb. Compression on the bulb leads to the injection of irritant liquid as the sharp tip facilitates its entrance into your epidermis. Stinging nettles in Hawaii lack the irritating chemicals. Why might this be advantageous?
		These are multicellular, non-secretory trichomes. It is not easy to characterize a trichome as secretory or non-secretory based on appearance alone. Secretory trichomes do have a characteristic anatomy, as you will see.
		This is a secretory trichome from Coleus, a member of the mint family (Lamiaceae). These and similar trichomes have a secretory head which is multicellular. In this case, the secretion builds up between the thin cuticle and the cell walls of the secretory cells. Eventually the cuticle will rupture and the volatile oils will be released. This is hastened if the leaves are rubbed. Most of the common culinary herbs from the Mediterranean have trichomes like these.
		A secretory trichome viewed with SEM. These can be stalked or sessile. Sessile trichomes only have the head cells.
		Inflorescence of Cannabis sativa. Note the many trichomes. Cannabis produces several different types of secretory trichomes on different structures. Some produce tetrahydrocannabinol which is an intoxicating substance. I once read that cannibanol was harvested by having sweaty natives run through the Cannabis fields naked. The cannabinol would stick to their skin and was scraped off for packaging and shipping.
		Cannabis plant showing its characteristic palmately compound leaves. There is some evidence that this plant produces substances which ease the nausea experienced by cancer patients. It is reasonable to conduct controlled, supervised scientific studies to see if this hypothesis has any validity. Our most effective pain killers originated with the opium poppy which is far more dangerous that these plants. Cannabis strains produce stem fibers like hau and flax. They are lignified and brittle and are used for the production of twine in the 3rd world.
		SEM images of Cannabis trichomes. Note the variety! Some are sessile while others are stalked.