190 TRANSLOCATION IN PLANTS 



all data are based on mass analyses of a mixture of tissues 

 and not of individual tissues and since they are expressed 

 as percentages of dry weight, further discussion of the 

 implications would seem unprofitable. 



Belval (1930), from analyses of banana material, came 

 to conclusions similar to those of Davis, Daish, and Sawyer, 

 that is, that sucrose is produced in the leaf, that this 

 enters the conducting tissues where it is progressively 

 transformed into hexoses which increase in amount at 

 greater distances from the leaves, and that sugars enter the 

 fruits as hexoses and are then transformed into starch. 



Weevers (1924) has determined the hexose and sucrose 

 contents of green and white parts of twelve difTerent kinds 

 of variegated leaves. His data are all expressed as per- 

 centages of dry weight. In only one of the twelve did he 

 find any reducing sugars in the white parts and in that 

 one the content was low as compared with the amount 

 in the green parts. The hexose gradient, therefore, 

 undoubtedly led from green to white parts. For sucrose, 

 six of the species showed higher contents in the green 

 parts, five showed higher contents in the white parts, and 

 with one there was no difference between the two. Since 

 the white parts had a higher water content than the green 

 parts, it is probable that several that showed a higher 

 sucrose content in the white parts when expressed as per- 

 centage of dry weight would have shown a reverse gradient 

 if expressed as percentage of water. The indications are, 

 therefore, that the sucrose gradient as well as that for 

 hexoses is in the direction of transport. 



Bruns (1925) has presented analytical data from leaf 

 tissues that have some bearings on sugar gradients and 

 transport. Using leaves of Helianthus and Nicotiana he 

 determined the sugar contents of the larger veins and those 

 of the mesophyll. Analyses were made of leaves immedi- 

 ately on harvesting after a bright day and of similar leaves 

 that had been stored in the dark for two days. Of those 

 stored in the dark some were stored as entire leaves while 

 others were separated into main veins and mesophyll. 



