TRICHOMES. 



69 



foot of the hair ma} T differ somewhat in shape, size, and arrange- 

 ment from the other epidermal cells. They may form an emi- 

 nence upon which the foot rests, or they may be somewhat 

 sunken so that the body of the hair 

 hardly reaches the general surface of 

 the epidermis ; but usually the hair 

 projects for a considerable distance 

 above the border of the depression. 



Both simple and compound hairs 

 ma}' be variously curved and 

 branched, giving rise to stellate and 

 man}' other forms. 



233. Scales are trie-homes which 

 are mostly compound, and consist 

 of discs borne by their ediires or cen- 



o 



tres, either with or without a short 

 foot or stalk. If the disc is com- 

 posed of radiating cells, the scale 

 becomes stellate, a form which re- 

 sembles or passes into the stellate 

 and tufted hairs common in Mal- 

 vaceae, etc. Well-marked stellate 

 scales are met with in Oleacea? and 

 Elajagnacere. 



234. Jlristles, prickles and epidermal spines are firmer or 

 stouter outgrowths. When such outgrowths are truly epidermal, 

 the} T come off with the epidermis. 



Hairs, scales, and prickles differ very greatly as to their per- 

 sistence, some being exceedingly short-lived, as, for instance, 

 the hairs which occur on roots ; while others, for instance the 

 prickles on the rose, last for long periods. 



235. In certain outgrowths from the edges of leaves or else- 

 where the structure is complicated by the presence of a portion 

 of the underlying framework. This is notably the case in the 



!/ fj 



fringe upon the leaves of Drosoraceye. There are all degrees of 

 variation between such trichomatous outgrowths and spinulose 

 teeth, or lobes. 



236. The consistence of the cell-wall in trichomes varies 

 widely, from extreme tenuit}' to the density of a silicified wall. 

 The more delicate hairs are transparent, so that the contents 



49 



FIG. 49. Branching unicellular bairs: a, from Humulus (the hop); b, stellate hair 

 of Deutzia. (Van Tieghem.) 



