158 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[31. 



ferous layer because it is the layer from which the root-hairs 

 (see p. 65), when present, are developed. Its cell- walls are not 

 cuticularised, but are frequently (especially in the root -hairs) 

 more or less mucilaginous. It is generally of but short duration, 

 and to be found only on the younger parts of roots which are the 

 regions of active absorption. 



In aerial roots (Orchids, etc.) where the epiblema persists as a 

 velamen (see Fig. 117, p. 155) of one or several layers of cells, 

 the walls are thickened, cuticularised (especially the superficial 

 layer), and somewhat lignified. 



lir 



FIG. 122. Hairs on a young ovary of 

 Cucurbita (x 100): b glandular hair; cef 

 early stages of development. 



FIG. 123. Root 

 hairs (h) on the 

 primary root (ic) 

 of a seedling of 

 the Buckwheat : 

 Tic hypocotyl ; c c 

 cotyledons. 



The many-layered root-cap (see p. 146), in its younger, more 

 internal part, consists of parenchymatous cells, with cell- walls of 

 cellulose, forming a compact tissue without intercellular spaces. 

 As the cells grow older, and come to be situated more externally, 

 they lose their protoplasmic contents. The disintegration of the 

 root-cap is due, in some cases, to the mucilaginous degeneration of 

 the middle lamella of the cell- walls ; whilst in other cases, where 

 the cell-walls become cuticularised, the superficial layers of the 



