500 



THE STRUCTURE OF ECONOMIC PLANTS 



cells of the parenchymatous sheath of the young rootlet. It forms 

 irregular areas and even broad zones, which are distinguishable from 



the surrounding tissue by 

 their lighter color. The 

 cells composing it are 

 commonly irregular, 

 /v^-^T'^^r^: .■•;...;. Q. •....-■. y I clongatcd, and poor in 



starch. The cells of the 

 bundle parenchyma are 

 polyhedral and fairly 

 uniform; they are very 

 rich in starch and possess 

 a well-developed nu- 

 cleus." 



Vascular Transition. 

 — The lower portion of 

 the hypocotyl is root- 



F.G. ^59. Diagrammatic transection of mature fleshy like in general plan. The 

 root. QAiter Artschwager, Jour. Agr. Res.) . "^ '■ 



primary xylem and 

 phloem are alternate and radial but the central portion of the 

 stele is parenchymatous. At successively higher levels, near the 

 middle of the hypocotyl, 



d9^o' 



^a 



o 



OOr 



latex vessel 



there is a gradual re- 

 orientation of the pri- 

 mary vascular tissue. The 

 four phloem regions are 

 divided into wide arcs 

 consisting of scattered 

 groups of phloem cells 

 which lie immediately 

 inside the pericycle and 

 alternate with the pri- 

 mary xylem points. The 

 metaxylem elements dif- 

 ferentiate in a tangential ^"^^^ss^^^yj^^'^^vM^ 

 position with respect to T /o^l 



the protoxylem so that 7;?'**'^'^^V___..-/^ 



each of the four xylem J-^^^ss-^^y 



poles consists of the pro- -^1 >s 



toxylem point with two 

 tangential arms of meta- 



O 



GO 



PoOq 



Op 



ooo^lpoo^ ^^m 



P%^oQ 



o. 



o 



sieve 

 tube 



O 



Oa 



.Or 



O 



O) 



b //Roo 



\Q 



O 



'd?- 



O 



Oi 



80000 







& 



a 



o, 



OqO 



^. 



0^ 



_oi 



^o 



Fig. 2.60. Transection of radial row of secondary 

 sieve tubes with companion cells and adjacent latex 

 xylem. (Fig. z6l. A.) vessel. (After Artschwager, /«/;•. ^^r. R^i.) 



