24 TRANSLOCATION IN PLANTS 



from the starch tests that the defoUated region, when 

 completely isolated from a source of supply by rings, 

 receives little or no carbohydrate. However, when isolated 

 from a source above only or from below only, the food 

 moves readily into the defoliated region. Both the dry 

 weights and the specific gravity calculations vary directly 

 with the starch contents as indicated by the iodine tests 

 and offer evidence, additional to that from the sugar 

 analyses presented in Table 2, that in experiments of this 

 type starch tests give a fair indication of the total amount 

 of carbohydrate present. 



Other experiments, in which defoliated and undefoliated 

 regions completely isolated by rings alternated with each 

 other, showed high starch contents in those regions bearing 

 leaves and a low content or complete absence in those 

 defoliated. The results from some such experiments are 

 reported on page 50. 



Knight (1801), though he made no direct tests for car- 

 bohydrates, observed the effects of the presence or absence 

 of leaves on the diameter growth of regions of the stem 

 completely isolated by rings. He observed not only the 

 effects of complete defoUation but also those of partial 

 reduction of leaf area, and found a direct relation between 

 amount of diameter growth and leaf area borne by the 

 isolated region. 



Swarbrick (1927) has suggested that these data on the 

 disappearance or appearance of starch between double 

 rings are not to be interpreted as related to the effects of 

 the rings on transport but to something that influences 

 cambial activity. As mentioned on page 32, however, he 

 fails to distinguish between depletion due to transport and 

 that due to utiUzation by living cells in the immediate 

 neighborhood. 



7. The Effect of Ringing on the Transport of Carbo- 

 hydrate to Growing Shoots after That Stored in the Xylem 

 Is Depleted. — In order to determine the channel of trans- 

 port to growing shoots, large numbers of vigorous leafy 

 shoots which had not completed terminal growth were 



