80 



THE BOOT, 



hy lengthening throughout every part; which is a characteristic 

 feature of the stem. 



132. The root, however, does not grow from its very apex, as is 

 commonly stated ; but the new formation (by continued multiplica- 

 tion of cells, 33) takes place just behind the 

 apex (Fig. 135), which consists of an obtusely 

 conical mass of older cells. As these wear 

 away or perish, they are replaced by the layer 

 beneath; and so the advancing point of the 

 root consists, as inspection plainly shows, of 

 older and denser tissue than the portion just 

 behind it. The point of every branch of the 

 root is capped in the same way. It follows 

 that the so-called spongioles or spongelets of 



the roots, or enlarged tips of delicate forming tissue, have no ex- 

 istence. Not only are there no special organs of this sort, but 

 absorption evidently does not take place, to any considerable extent, 

 through .the rather firm tissue of the very point itself 



133. Absorption by Roots. As the surface of the root, like every 

 part of a plant, consists of closed cells, it is evident that the moist- 

 ure it so largely takes in must iss 

 be imbibed through the walls of 

 the cells, by endosmose (40) ; 

 and that the whole surface of a 

 fresh root will take part in ab- 

 sorption. The newer the root, 

 however, the more actively does 

 it absorb, the cells then having 

 thinner walls. As they become 

 older, the superficial layer of 

 cells thicken their walls and 

 form a kind of skin, or epider- 

 mis (69), tlirough which absorp- 

 tion does not take place so free- 

 ly. Roots accordingly absorb mostly by their fresh tips and the 

 adjacent parts ; and these are constantly renewed by growth, and 



FIG. 135. The tip of the root of a seedling Maple (Fig. 106), magnified : o, the place where 

 growth is mainly taking place, by cell-multiplication : 6, the original tip of the radicle. 



FIG. 136, 137. Portions of the surface of the same, highly magnified, showing the nature 

 of the root-hairs or fibrils. 



