188 



TRANSLOCATION IN PLANTS 



tubes is correlated with its diffusion gradient. A detailed 

 discussion of concentration gradients and their bearing 

 on the transport by protoplasmic streaming are considered 

 in Sec. 35 and also partly in Sec. 42. 



35. The Relation of Concentration Gradients to Trans- 

 port. — Although Mason and Maskell appear to be the first 

 investigators to give data that can be safely interpreted 

 as indicating real concentration gradients, it seems desirable 

 to consider briefly the works of a few others which give 

 data that show indications of concentration gradients 

 that can be compared with the findings of Mason and 

 Maskell who have restricted their investigation to the 

 cotton plant. Sachs (1863), Schimper (1885), Rywosch 

 (1908, 1909), and others have observed the order of empty- 

 ing and filling of leaves or storage organs and have inter- 

 preted these in terms of gradients, but they are of little 

 help in the problem before us. 



From results of many analyses of leaf blades, midribs, 

 and stalks of several plants, but principally the mangold 

 and potato, Davis, Daish, and Sawyer (1916) conclude 

 that sucrose is the primary product of photosynthesis in 

 all leaves and that this is introduced into the conducting 

 tissue where, during transport to storage roots or tubers, it 

 is gradually transformed into hexoses. They suggest 

 that the sugar is finally absorbed as hexose by the storage 

 organs, in the cells of which it is converted into the storage 

 product, starch, inuhn, sucrose, etc. Their analyses of 

 leaf blades, midribs, and upper and lower parts of the leaf 

 stalks showed a progressive increase of hexoses and a slight 

 decrease in sucrose, with a marked decrease in proportion 

 of sucrose to hexose. One set of analyses for sugars in the 

 mangold showed the following contents expressed as 

 percentage of dry weight at 4 p.m. 



Sucrose . 

 Hexose . 



Stalk 



5.26 

 26.30 



