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AMERICAN JOURNAL O? BOTANY 
[Vol. 8, 
of the endodermis and that of the root tip. It may be that in the absence 
of root pressure and in the presence of a negative pressure in the vessels, 
water and solutes may pass through the endodermis and through the root 
tip in a purely physical manner. Evidence also exists to support the view 
that certain amounts of salts are concentrated in the leaves, and it is possible 
that these salts are thrown out of solution by the protoplasm so as not to 
upset the osmotic relation of the cells. The assumption that solutes are 
adsorbed by the living protoplasts accompanying the vessels is also sug- 
gestive. 
Whatever ma}^ be the mechanism of the entrance of solutes into the 
root and of their passage into vessels, it would appear that the problems 
here stated are worthy of serious and careful investigation. 
Department of Botany, 
University of Wisconsin 
