452 



BOTANICAL GAZETTE 



[DECEMBER 



in addition thick-walled fibers constituting the so-called hard 

 bast). The parenchymatous elements are in turn plainly of two 

 kinds: large cells containing starch grains, which are represented 

 in black as if stained with iodine, and much smaller, starchless 

 elements. The latter are the companion cells, whereas the former 

 are ordinary storage parenchyma. A further difference between 

 the two kinds appears in longitudinal sections; the companion 

 cells are highly elongated vertically, while the ordinary storage 

 parenchyma cells are rectangular. It should be noted that a 



Fig. I. — Mature bast of Aristolochia macrophylla (Lam.); Xiooo 



companion cell is associated with each sieve tube and is frequently 

 fitted snugly into one corner of the tube. 



The bast of Aristolochia was chosen for illustration because 

 its elements exhibit a more orderly arrangement than is usual in 

 angiosperms. In many species the rows of phloem cells formed 

 at the cambium very quickly become so distorted that the orderly 

 sequence is lost, and the cells of the mature bast then appear to 

 be haphazardly placed. In Aristolochia, however, the rows of 

 cells are to a certain extent preserved in the mature bast, as may 

 be seen in fig. i. When this is the case, there is a significant 



