62 



STKUCTURE OF ROOTS. 



ROOT OR DESCENDING AXIS. 



Structure of Roots. 



119. In the young state there is no distinction between stem and 

 root, as regards structure; both being cellular, and an extension of 

 each other in opposite directions. In stemless plants, as Thallogens, 

 the root remains in a cellular state throughout the life of the plants. 

 The root is afterwards distinguished from the stem, by the want of 

 a provision for the development of leaf-buds, and by increasing from 

 above downwards. Some plants, however, as the Moutan Pasony, the 

 Plum-tree, Pyrus japonica, and especially Anemone japonica, have a 

 power of forming buds on their roots. The last-mentioned plant 

 developes these buds on every part of its extensively ramifying roots, 

 which may be chopped into numerous pieces, each capable of giving 

 rise to a new plant. The part where the stem and root unite is the 

 collum or neck. In woody plants, the fibres of the stem descend into 

 the roots, and there is a similar internal arrangement of woody layers, 

 as is seen in the stem itself. 



120. Roots are usually subterranean and colourless. Externally, 

 they have a cellular epidermal covering of a delicate texture, some- 

 times called epiblema (^[ 47), in which no stomata exist. Their in- 

 ternal structure consists partly of cells, and partly of vascular bundles, 



in which there are no vessels with fibres 

 which can be unrolled. Roots do not ex- 

 hibit true pith, nor a medullary sheath. 

 The axis of the root gives off branches 

 which divide into radicles or fibrils (fig. 119), 

 the extremities of which are composed of 

 loose sponge-like cellular tissue, and are 

 called spongioles or spongelets. Over these 

 a very thin layer of cells is extended, 

 called, by Trecul, a Pileorhiza (y/xo?, a 

 cup, and ^, a root). This sometimes 

 becomes thickened, and separates in the 

 form of a cup, as in Screw-pines (fig. 115, 

 2), and in Lycopodiums. Occasionally 

 the extremities of roots are enclosed in a 

 sheath, or ampulla, as in Lemna. Cellular 

 papillae and hairs are often seen in roots 

 (fig. 77), but no true leaves. Roots do not 

 grow throughout the whole length like stems, but by additions to their 



119 



Fig. 119. Tapering root of Malva rotumlifolia, giving off branches and fibrils. 



