ANGIOSPERMS. 



591 



has not also taken place in the hypophysis (h); but finally it takes place in it 

 also and in such a way (as is shown in Fig. 403, V) that the upper of its two 

 cells breaks up into two layers {h'), the outer of which becomes continuous with 

 the dermatogen of the axis, while the inner layer forms a prolongation of the 

 internal axial tissue. The lower cell of the hypophysis {h) divides cross-wise 

 {V b, seen from below) and may be regarded as a transitional structure between 

 suspensor and root (appendage of the root) or as the first layer of the root-cap. 

 The root-cap is formed in this case simply by a luxuriant growth of the dermatogen. 

 The dermatogen, which elsewhere remains simple, and passes over into permanent 



Fig. 403.— Development of the embryo of Capsella Btirsa-pastorts (after Hanstein) ; I— VI various stages of 

 development, F* apex of the root seen from below; i, r, 2, 2, the first divisions of the embryo-cell, h h the hypophysis, 

 ■V the suspensor, c the cotyledons, s apex of the axis, lu root (the dermatogen and plerome are shaded). 



tissue in forming the epidermis, increases in thickness, on the contrary, where it 

 covers the punctum vegetationis of the root, and undergoes repeated periclinal divi- 

 sions (parallel to the surface). Of the two layers which are successively formed 

 on each of these occasions, the outer becomes a layer of the root-cap (Fig. 404 

 wh, and Fig. 405, 2) ; the inner remains as dermatogen and again undergoes the 

 same process. This dermatogen which covers the vegetative cone of the root 

 behaves therefore like a layer of phellogen, with this difference, that the cells 

 produced from cork-cambium become at once permanent cells, while those of 

 the root- cap remain still capable of division ; so that each layer split off as it 



