416 BOTANICAL GAZETTE [ DECEMBER 
ness to the plant of sodium as a chemical, this conclusion is 
still surprising. The phenomenon of turgescence is explicable 
by purely physical laws, and is dependent on the vitality of the 
plant only for the semi-permeable membrane, the living proto- 
plasm differentiated as ‘‘ Hautschicht.” And yet, here where 
the physical properties of sodium would seem to give it a dis- 
tinct advantage over the heavier potassium, leaving out of con- 
sideration the relative scarcity of the latter, we find the plant’s 
insistence on potassium as decided as it is for the vital processes 
of growth and photosyntax. Indeed, in many instances (Phase- 
olus, Pisum) the effect of want of potassium appears in the 
turgor, while growth still continues normal. The plant can 
exhaust to the last trace the potassium of its substratum, yet it 
was found in appreciable quantity in the cell-sap of plants 
whose protoplasm was dying for want of it ; as Zea (3a and 3b) 
after a large part of the plant was brown and dry still showed 
its highest turgor in the parts still living. Though the living 
plasma may bound itself toward the cell sap with the same 
‘‘Plasmahaut ”* which it opposes on the other side to its 
environment, yet the vacuole is physiologically as truly a vital 
part of the cell as is the alimentary canal an essential part of the 
human being. 
The laboratory work whose results are embodied in this paper 
was performed at the University of Wisconsin in the laboratories 
of Professor Barnes and Dr. Kahlenberg, to whom I wish to 
express my sense of obligation for the admirable equipment 
placed at my disposal, and for their kindly assistance at all 
times. 
UNIVERSITY OF INDIANA, BLOOMINGTON. 
* W. Pfeffer: Zur Kenntniss der Plasmahaut und der Vacuolen, etc. Leipzig. 
T1890. 
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