72 



PLANT LIFE. 



bundles are of two kinds, xylcm bundles a.wA phloem bundles, 

 so placed that they alternate with each other about the 

 periphery of the stele (figs. 86, 88, 89). The xyleni bundles 

 may be in contact with one another in the center, or the 

 center of the stele may be occupied by a inth (figs. 86, 89). 



Fig. 86. — Transverse sectirm of (he stele <iiid a portion of the surrounding cortex of the 

 root of calamus, s, s, innermost layer of torte.x, the endodermis, adjoirring outermost 

 layer of stele, the pericycle; /. xylem bundles; ///, phloem bundles. The shaded ele- 

 ments of xylem bundles are the ininiary xylem ; the large ones, ,t,', are secondary. In 

 the center of the stele and between the bundles is conjunctive tissue. Highly magnified. 

 — After .Sachs. 



The tissues of the .xylem are usually lignified (see "j 9) 

 and, when abundant, make up \N'liat is called the zcoix/. They 

 aie the chief water-conducting elements of the older parts of 

 the root. 



The tissues of the phloem are usually' not lignillcd, and the 

 most iin|iortaut ones are the sicTc-Zii/n-s. which conduct pr(.)teids 

 from al.>o\e to the growing regions of the root. 



