SOLUTE DISTRIBUTION AND BEHAVIOR 247 



would be favored by an adequate water supply. They 

 could therefore use carbohydrates faster, which would 

 steepen the gradient leading to them, and their increased 

 activity might also favor more rapid streaming in the 

 connecting phloem tissues. A similar explanation would 

 apply to many other instances given by Loeb and others, 

 where one active tissue becomes and remains dominant 

 over others. 



This hypothesis might also well explain the seeming 

 conflict between the two concepts that solutes move to a 

 tissue because it grows and that a tissue grows because 

 solutes move to it. Any treatment that starts the activity 

 of a group of cells, as in a shoot or root meristem or in a 

 fruit or storage tissue, may establish a diffusion gradient 

 leading to these cells and also initiate the streaming 

 activity of the conducting cells leading to this particular 

 region, thus establishing an active conducting system con- 

 necting the meristem or storage tissue with a supply of 

 necessary solutes. The supply of these solutes to the 

 particular tissue enables it to continue its activity and 

 thus also to continue its connection with the source of 

 supply. The solutes, therefore, move to this tissue because 

 the tissue is active, and the tissue may remain active 

 because foods are moving to it. The original activity 

 may be initiated either by a greater supply of foods or 

 other solutes or by any one or more of various other 

 agents. The increased nitrogen absorption as well as the 

 increased photosynthetic activity in plants sprayed with 

 bordeaux, as reported by Mader (1934) and others, may 

 be in part due to an effect of copper increasing the effec- 

 tiveness of the translocation mechanism. This agrees 

 nicely with the streaming hypothesis, for it is well known 

 that traces of copper are highly effective in inducing or in 

 hastening protoplasmic streaming. 



The mechanism of food movement as proposed by Miinch 

 (1930) can also be adapted, as he suggests, to account for 

 dominance. According to his hypothesis a receiving cell 

 can cause materials to flow to it by keeping a low osmotic 



