454 



BOTANICAL GAZETTE 



[DECEMBER 



lower part of the figure into the bast of the upper part, it becomes 

 perfectly clear that each sieve tube and its companion cell are 

 derived from contiguous cells in the same row, and that as the 

 bast matures the companion cell tends to become shifted to one 

 corner of the sieve tube. I have not been able to show that sieve 

 tube and companion cell are products of one division. In fact, 

 judging from what we know of cambial activity, it seems more 

 probable that they are products of two successive divisions, in 



Fig. 3.— Mature bast of Gnetum latifoliiim showing sieve tubes and companion 

 cells; Xiooo. 



each of which one daughter (the innermost) remains cambial. 

 In other words, they are probably not sisters but aunt and niece. 

 However that may be, for the purposes of the present discussion 

 the important conclusion is that they are successive members of 

 a single row of cambial products. 



Companion cells of Gnetum 



The mature bast of several species of Gnetum (fig. 3) consists 

 of only two kinds of elements, large clear sieve tubes and small 

 parenchymatous cells. The latter evidently correspond to the 



