FORMS OF ROOTS. 



65 



plants, the young root or radicle pierces the lower part of the axis 

 (fig. 124 r), is covered with a cellular sheath, c, and gives rise to 

 numerous fibrils, r' r' r' r', which are similarly developed. These 

 plants are therefore called by Eichard, Endorhizal (svlov, within); 

 and the sheath is denominated Coleorhiza (xoheos, a sheath). In their 

 after progress, they usually retain their compound character, con- 

 sisting of fibrils, most of which often remain unbranched (figs. 120, 121). 

 The first-formed roots which surround the axis, if the plant is peren- 

 nial, gradually die, and others are produced in succession farther 

 from the central axis. In Endogenous roots, the same structure is 

 observed as in the stem. Thus, fig. 125 represents a section of a 



Palm root, composed of cellular tissue, porous vessels, v p, scalari- 

 form vessels, v s, fibrous or woody tissue, f, and laticiferous vessels, I. 

 Eoots are pushed out from various parts of the stems of many Palms, 

 and ultimately appear as part of the external integument. 



128. Root of Acolj Icdonous or Acrogenous Plants. In these plants, 



the young root is a development of superficial cells from no fixed 

 point, and they have been called Heterorhizal (er^os, diverse). In 

 their subsequent progress, these roots present appearances similar to 

 those seen in the stem. They frequently appear in the form of fibres 

 on the outer part of the stem, giving rise, by their accumulation at the 

 base, to the conical appearance represented in fig. 116 r a. 



Fig. 124. Grain of wheat germinating. <7, The mass of the grain, t, The young stem begin- 

 ning to shoot upwards, r, The principal root of axis. i j r 1 r 1 r 1 , Lateral roots, covered like the 

 preceding, with small hairs or threads, c c c, Coleorhiza or sheath, with which each of the roots 

 is covered at its base, while piercing the superficial layer of the embryo. 



Fig. 125. Transverse section of part of the root of a Palm (Diplothemimn maritimum), to show 

 the mode in which the cells and vessels are arranged, v p, Large porous vessels situated in the 

 interior, v s, Scalariform vessels more external, and becoming smaller the farther they are from 

 the centre. /, Fibrous tissue, or elongated cells, accompanying the vessels. I, Groups of latici- 

 ferous vessels of different sizes, the larger being inside. 



F 



