THE CENTRAL CYLINDER 



113 



thin-walled cells 

 in close union 

 with the endoder- 

 mis : at certain 

 points on this lay- 

 er the woodj- and 

 the liber fasci- 

 cles appear, tin- 

 latter alternating 

 with the former 

 throughout the 

 circle, and the 

 spaces between 

 them being filled 

 with parenchyma. 

 337. The num- 

 ber of fibro-vas- 

 cular bundles in 

 the central cj'lin- 



der varies accord- 

 ing to the class of 

 plants, and in the 

 same plant accord- 

 ing to the age and 

 size of the root. 

 There are generally 

 two in Cruciferae, 

 often three in Er- 

 vum Lens, four in 

 Ricinus,five in Vicia 

 Faba, six in Alnus, 

 and eight in Fagus ; 

 but these numbers 

 are bj' no means 

 constant. 



338. The woody 

 part of the bundle 

 may become re- 



FIG. 91. Transverse section of the central cylinder of a root of a monocotyledon (Colc- 

 casia antiqnorum) : e, internal layer of the proper cortex ; p, endodennis; in, j>eripheral 

 layer of the cylinder; /, liber fascicles; v, woody fascicles; c, conjunctive parenchyma 

 (pith and medullary rays). (Van Tieghem. ) 



FIG. 92. Transverse section of tlie cent ml cylinder of a root of a dicotyledon (Artanthe 

 elongata) : e, internal layer of the proper cortex; p, endodennis; m, peripheral layer 

 of the cylinder; /, liber fascicles; r, woody fascicle; c, conjunctive parenchyma (pith 

 and medullary rays). (Van Tieghem.) 



