166 



PART II. -THE INTIMATE STRUCTURE OF PLAKTS. 



[ 32. 



which case the endodermis can, in many cases, be distinguished 

 by the presence of starch-grains in its cells. 

 When the endodermis is double, this marking is 

 confined to the outer of the two layers. 



This marking is not confined to the endodermis ; 

 it sometimes occurs also in the exodermis of 

 roots (see p. 161), and in one or more layers of 

 the internal cortex in some roots (one layer, next 

 the endodermis, in Cupressus, Taxus, Prunus, 

 Rosa, Lonicera, etc. ; several layers, Juniperus, 

 Sequoia, many Cruciferse such as Mustard and FlG 128 ._A cell 



Wallflower). from the internal 



The wajls of the endodermal cells frequently %,*&* 



become sclerotic either over their whole surface, obliquely from the 



or more frequently on the internal and lateral internal surface, 



surfaces (Fig. 129). When this is the case, some berised" thickening 



of the cells remain thin- walled, as passage-cells, zone - (After van 



., -i i -11 :-, . Tieghem: x 350.) 



opposite to the wood-bandies within. 



The Intra-stelar Fundamental Tissue, or Conjunctive Tissue of the 



Stele. Morphology. The morphology of the conjunctive tissue, 



of the stele varies somewhat in 

 accordance with the develop- 

 ment of the vascular tissue. 

 When a solid vascular cylinder 

 is produced, there may be no 

 conjunctive tissue at all, the 

 whole of the plerome having 

 developed into vascular tissue ; 

 or the conjunctive tissue may 

 be limited to one or more peri- 

 pheral layers, the pericycle, in- 

 vesting the vascular cylinder; 

 or, again, in addition to the 

 pericycle, the conjunctive tissue 

 may extend inwards to some 

 FIG. 129. Part of a transverse section of extent between the bundles (in- 



a root ofirisjiorent.na; e sclerotic endo- terfoscicular) of the stele ; on the 



dermis, with / a thin- walled passage-cell; _ 



bast; 8 wood-vessel; c cortical ground- other hand, when the vascular 



tissue; p pericycle. (After Strasburger: cylinder is hollow (see Fig. 



130), the central space is oc- 

 cupied by medullary conjunctive tissue, constituting the pith, and 



