THE ROOTS 



4 1 



the vascular cylinder retains its freshness, even in the case of the delicate 

 seminal rootlets, during almost the whole life of the plant. 



In roots from which the cortex has decayed, the endodermis, pericycle, 

 and conjunctive parenchyma of the stele becomes very strongly sclerotic, 

 but the cells of the bast and the 

 xylem vessels preserve their normal 

 character (Fig. 29). 



The anatomy of the stronger 

 adventitious roots which spring 

 from the nodes of the stems at or 

 just above the surface of the soil 

 differs in certain points from that 

 of the seminal or thinner adven- 

 titious roots. The exodermis 



f> 



is 



FIG. 29. Transverse section of a portion of 

 the vascular cylinder of an old seminal root 

 examined in May ( x 260). c, Cortex ; e, 

 endodermis ; p, pericycle ; b, phloem. 



often more persistent, and imme- 

 diately within it there is frequently 

 developed a zone of sclerotised 

 cortical cells two or three cells thick (Fig. 30), which, for a time, protects 



c 



d 



FIG. 30. Transverse section of a portion of an adventitious root from the node imme- 

 diately above the soil surface ( x 1 50). ex, Exodermis ; h, thick-walled cortical cells ; c, 

 thin-walled cortical cells containing chloroplasts ; e, endodermal cell with thick inner 

 wall ; e', thin-walled endodermal cell ; d, lignified pericycle. 



the turgid cortex within from collapsing. In the cells of the thin-walled 

 cortical parenchyma of the stout adventitious roots arising from nodes just 

 above the soil surface, numerous chloroplasts are found, especially in the 

 inner layers, the central cylinder then appearing to be surrounded by a 

 zone of green tissue. 



