IPOMOEA BATATUS 



499 



walls and differ in this respect from plants having a latex system 

 in which a continuous 

 tube is formed by the 

 resorption of the end 

 walls. (Fig. x6o.) The 

 prominent latex vessels 

 may be recognized in 

 young tissue by their 

 large size and by their 

 white viscid contents in 

 which oil droplets are 

 in suspension; but in 

 older tissue, they are 

 less readily identified 

 owing to the increased 

 size of the adjacent 

 cells. The elements of 

 the secondary xylem 

 consist of both wide 

 and narrow vessels in 

 which the vessel seg- 

 ments are intercon- 

 nected by a single large 

 pore. The walls are 

 pitted and tyloses fre- 

 quently develop in the 

 larger vessels. 



Artschwager (i) clas- 

 sifies the storage paren- 

 chyma under two types : 



"Qa) normal bundle 

 parenchyma which, like 

 the xylem and the 

 phloem, is a product of 

 the cambium; (b) in- 

 terstitial parenchyma — 

 a filler between the 

 groups of bundles. The 

 interstitial parenchyma 

 can be considered the 

 direct progeny of the 



— ca 2 



Fig. 2.58. Transection of portion of fleshy root about 

 10 mm. in diameter : ca, cambium ; ca 2., secondary 

 cambium ; co, cortex ; Ix c, latex cell ; Ix ves, latex 

 vessel ; pd, periderm ; ph z, secondary phloem ; xy 1, 

 secondary xylem. (After Artschwager, Jour. Agr. Res.^ 



