THE CENTRAL CYLINDER. 



Ill 



tliin-walled cells 

 in close iiuiou 

 Tv-ith the endoder- 

 mis ; at certain 

 points on this lay- 

 er the woody and 

 the liber fasci- 

 cles appear, the 

 latter alternating 

 with the former 

 throughout the 

 circle, and tlie 

 spaces between 

 them being filled 

 with parenchyma. 

 337. The num- 

 ber of fibro-vas- 

 cular bundles in 

 the central cjlin- 



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 Cruciferag, 

 often three in Ev- 

 vnm Lens, four in 

 Ricinus,five in Vicia 

 Faba, six in Alnus, 

 and eight in Fagus ; 

 but those numbers 

 are b^' no means 

 constant. 



338. The woody 

 part of the bundle 

 may become re- 



FiG. 91. Transverse scclioTi of the central cylinder of a root of a monocotyledon (Colo- 

 casia aiitiqnoruni) : e, internal layer of tlie proper cortex; p, cndodermis; ?u, periplieral 

 layer of the cylinder; /, liber fascicles; i', woody fascicles; c, conjunctive parcncliyma 

 (pitli and medullary rays). (Van Tiegliem.1 



Fig. 92. Transverse section of tlie central (iylinder of a root of a dicotyledon (Artanthe 

 elongata) : e, internal layer of the proper cortex; />, endodermis; m, peripheral layer 

 of the cylinder; I, Uber fascicles; 7-, woody fascicle; c, conjunctive parenchyma (pith 

 and medullary raj s). (Van Tieghcm.) 



