132 



STRUCTURAL BOTAXV 



outer surface, into an inner and an outer cell. The 

 eight outer cells thus cut off form the dermatogen of 

 the embryo (see Fig. 46, C, d). Their further divisions 

 take place entirely by walls at right angles to the 

 surface, so that the layer remains one cell thick. It 

 gives rise to the entire epidermis of the shoot, and to 



no other tissue. The 

 eight inner cells then 

 divide in their turn, 

 forming a central group 

 and an intermediate 

 layer (see Fig. 46,D). 

 The central group be- 

 comes the plerome, 

 from which the central 

 cylinder of the main 

 stem is developed, while 

 the intermediate layer 

 between plerome and 

 dermatogen becomes 

 the periblem, from 

 which the cortical 

 tissues arise. 



The last cell of the 

 Other letters suspensor immediately 

 Ma S- adjoining the embryonic 

 cell also contributes 

 something to the formation of the embryo. It divides 

 by a transverse wall, and the daughter-cell next the 

 embryonic cell by its further divisions forms the root- 

 cap and periblem of the root (see Fig. 47, r.c. and r), 



FIG. 47. Older stage of same ; the 

 two cotyledons now project beyond 

 the growing point, r, periblem of 

 root; r.c, root-cap, 

 as before. (After Hanstein.) 

 nified about 200. 



