BOTANY 



PART I 



protoplasm, becomes the stoma mother cell ; while the larger, containing less 

 protoplasm, usually forms an ordinary epidermal cell. The stoma mother cell 

 becomes elliptical in outline and divides again, by a vertical wall, into the two 

 guard cells, between which, by a splitting of the wall, the intercellular passage 

 (pore) is formed. Before the formation of the definite stoma mother cell, succes- 

 sive divisions of the young epidermal cell often occur ; in such cases the finally 

 developed stoma is generally surrounded by subsidiary cells. 



3. HAIRS. The epidermis of almost all plants bears hairs 

 (trichomes). They are sometimes . unicellular structures and form 



papillate (Fig. 50), tubular (Fig. 

 51), or pointed (Figs. 52, 55, 56 

 to the left) protrusions of the 

 epidermal cells. In other cases 

 they are multicellular and form 

 cell rows (Fig. 5), stalked or 

 unstalked cell surfaces (scale- 



FIG. 50. -Surface of the upper epidermis of a petal hairs, Fig. 54) which may re- 

 of Viola tricolor, showing ridge-like infoldings semble Small leaVCS as in the 



' papillae ' ramenta of Feras > or cel1 masses - 



The multicellular trichomes are 

 also developed from .young epidermal cells, and, indeed, usually 

 proceed from a single initial cell of the hair by its growth and 

 subdivision. Unicellular and multicellular hairs may further be 

 unbranched or branched (Fig. 53, stellate hairs). Their walls may be 



FIG. 51. Epidermis of the root in longitudinal section showing root-hairs (B) 

 and their origin (,4). (After ROTHERT, semi-diagrammatic.) 



thin and delicate or strongly thickened and frequently calcined or 

 impregnated with silica, and sharply pointed at the tip (bristles, Fig. 

 55, right). The protoplasts may remain alive and resemble those of 

 the epidermal cells, or may die. In the latter case the cavity often 

 becomes filled with air and the hair appears white, or it may be 

 laterally compressed as in the case of the long hairs of the cotton-seed 

 (Fig, 52) from which the cotton of commerce is obtained. The basal 

 portion of the hair in the epidermis may be distinguished from the 



