PLATE XXXVII. 



Fig. 7. Tangential section of Populus alba, showing the "beaded" end 

 plate of a sieve tube and starch granules in the slime body. 



Fig. 8. Tangential section in the root of Populus deltoides, showing one 

 of the remarkable obliquely placed end plates of a sieve tube in 

 cross section. The strengthening bands here appear as larger 

 beads and the perforation of the wall as spaces between 

 smaller beads. This long plate evidently gives more surface 

 for the distribution of the pits and possibly better communi- 

 cation between the two cells of the sieve tube. 



Figs. 9 and 10 are from tangential sections of the root of Populus del- 

 toides, and show the reticulated markings caused by the pit- 

 ting and banding of the obliquely placed end plates in the 

 sieve tubes. In figure 10 the sieve tube adjoins a medullary- 

 ray cell. 



