106 



BOTANY 



PART I 



described (Fig. 115) in the possession of a root-cap. The dermatogen 

 (d) and periblem (pr) unite at the apex in a single celldayer, outside 

 of which lies the calyptrogen (k) or layer of cells from which 

 the root-cap takes its origin. In many other roots, however, the 



Fi(!. 117. — Meciian longitudinal section of the apex of a root of the Barley, Hordeum imlgare. Tc, 

 Calyptrogen ; d, dermatogen ; c, its tliickcne<l wall ; pr, periblem ; pi, plerome ; en, endoderniis ; 

 i, intercellular air-space in process of formation ; a, cell row destined to form a vessel ; r, 

 exfi>liated cells of the root-cap. (x ISO.) 



formation of the root-cap results from the periclinal division of the 

 dermatogen itself, which, in that case, remains distinct from the 

 pei'i])lem. In the apices of Gymnosperms the dermatogen, periblem, 

 and calyptrogen are not marked out as distinct regions. In roots, 

 as in stems, the plerome cylinder (jjI) almost always terminates in 

 special initial cells. 



