SPOROPHYTE. 



13 



walls are brownish-yellow, like those of all of the cells outside of the 

 endodermis. The subjacent hypodermal cells are about three times as 

 wide and twice as deep radially as those of the epidermis, and similarly 

 elongated. The first cortical layer is composed of cells nearly twice as 

 larg-e in cross-section as the foregoing, but like the last in length and 

 character of wall. Intercellular spaces occur rarely at the angles of these 

 cells. The cells of the second cortical layer are smaller again, often as 

 narrow as the epidermal cells. The two innermost layers are still smaller. 

 In the last three layers, especially the middle one, thickening of the walls 

 begins even before the root hairs are fully mature (fig. 43). At this stage 

 the endodermal cells are already very long, narrow, and practically empty. 

 Pericycle and conjunctive parenchyma are full of dense, granular contents. 

 They are probably multinucleate, since the cells are very narrow and long, 

 but nearly always show a nucleus in cross-sections. The pericycle cells are 

 often much larger in the region of the protophloem than elsewhere (fig. 

 35). The protophloems have already passed their greatest density and 

 prominence and the sieve-tubes now appear mature. Each protoxylem 

 consists of one or two extremely slender spiral elements, with one or two 

 slightly wider scalariform tracheids on either side. The two or four large 

 central tracheids of the metaxylem show as yet no thickening of the walls 

 (figs. 34, 35, 36, 43,44). 



TABLE 4. Statistics of transverse section of root. 



* Immature. flections of one root, 16 ^ apart. 



Following all these parts upward in an old root, we find that the epider- 

 mis and outer soft layer of cortex wither after the root-hairs die, and are 

 ultimately sloughed off (fig. 46). The bundle is now protected by the 

 two or three inner cortical layers, whose walls have thickened so as almost 

 to obliterate the lumen. Lignification in the metaxylem takes place slowly. 

 In a section showing a withering epidermis, and the inner cortex indurated 



