gg MORPHOLOGY OF THE CELL. 



the leaves of many species of Peperomia, Ficus, and Begonia. 

 Multiple epidermis is not always of even thickness throughou t; 

 sometimes a portion may be only one or two cells thick, while 

 adjacent portions are composed of many layers. Such differ- 

 ences are generally associated with the occurrence of stomata, 

 hairs etc The subjacent cells in some forms of multiple epi- 

 dermis are smaller than those above them, and in these cases 

 the arrangement of the cells in the successive layers presents 



striking inequalities. 



230. Trichomes. tinder 

 this term are included the 

 multifarious forms of hairs, 

 scales, bristles, and prickles. 



Hairs are sometimes of 

 diverse forms on the same 

 plant, and even on the same 

 part, but sometimes so pecu- 

 liar and uniform throughout 

 large genera, or even orders, 

 that they aid in their iden- 

 tification; as, for instance, 

 in Malpighiacese, Loasacese, 

 and Elaeagnaceae. 



231 . Simple hairs, whether 

 branched or unbranched, are 

 formed by the prolongation 

 of a single epidermal cell, 

 either slight, forming a 

 mere papilla, or to a great 

 length, as in the so-called 

 fibres of cotton. Simple 

 hairs are abundant upon the 

 rootlets of most plants at a 

 little distance behind the ad- 

 vancing tip, where they play an important part. 



232. Compound hairs are of all degrees of com- 

 plexity. They may start from a single cell, or from 

 a group of cells, and may have the derivative cells 

 47 a arranged in many ways. The cells at or near the 



FIG. 47 a. Upper portion of a glandular hair of Martynia proboscidea. T- (Martinet ) 

 PIG. 47 t>. View from above, of the upper portion of the same. ?". (Martinet ) 

 FIG. 48. Cynoglossum officinale. Longitudinal section through a young angular 

 bristle at the beginning of the thickening. =4*. (Strasburger.) 



