COURSE OF FOOD DISTRIBUTION 165 



where the sieve tubes occur, it is plain that a slow movement 

 in the many veinlets could feed a much more rapid flow in the 

 few main channels; and this is presumably what happens. 



FIG. 91. -Showing the effect of cutting across the veins on the removal of food from 

 the leaf. A, all of the main veins are cut across near their bases; B, the mid-vein alone has 

 been severed. The stippled areas indicate the starch reaction with the iodine test. (After 

 Mary Blue.) 



