KOOT APEX OF BARLEY. 



221 



in common initial cells, or histogens. In our figure only two 

 such common initial cells are present, but there may be several. 

 The dermatogen, as such, can be traced up to the^e initials ; 

 and the periblem also, only one cell thick, impinges upon them. 



FIG. 87. Median longitudinal section through the root-apex of Hordeum vulgare. 

 k, calyptrogen ; c, thickened outer wall of the epidermis ; d, dermatogen ; pr, peri- 

 blern ; pi, plerome ; en, endodermis ; i, intercellular passage filled with air ; a, row 

 of cells which will form the central duct ; /, disorganised cells of the root-cap (x 180). 



The plerome under this common dermatogen-periblem cap, ends 

 in its own initial cells. Outside the line which separates the root- 

 body from the root-cap are the initial cells for the root-cap, form- 

 ing a layer of flattened cells which may be designated the calyp- 

 trogen (k). The cells which are given off outwardly from the 



