— : ces just overcomes th 
234 BOTANICAL GAZETTE [SEPTEMBER 
with the permeability of a membrane considerably different from 
the plasma membrane. Loe suggests the theory that the dye 
kation is held in the membrane in a combination with a colloidal 
anion, and that this combination is broken down by the anions of 
a surrounding salt solution. The behavior of the potassium ion 
is shown to be like that of the dye kation, at least in its initial stages. 
Similar processes may occur in the plasma membrane, but it is 
not possible to apply Lors’s conclusions directly to the behavior of 
unspecialized protoplasm 
Harvey (12) has siuidied the permeability of plant cells to 
alkalies by introducing an intra-vitam stain, neutral red, which 
turns yellow in the presence of alkalies It was found that 
ammonia and the amines penetrated living and dead tissues with 
equal and very great rapidity, while the strong bases, although 
penetrating dead cells with great rapidity, required much longer to 
penetrate living cells. It seems possible that penetration of bases 
at the concentration used (0.025 N) was due to injury of the cells. 
Turgidity of cells or tissues 
The typical living cell behaves toward osmotically active solu- 
tions as though it were surrounded by an elastic semipermeable 
membrane. In view of the widespread confusion regarding the 
osmotic relations of living cells, it seems necessary to analyze, in 0 
far as the present imperfect state of our knowledge of the physical 
laws governing osmotic phenomena will allow, the behavior of @ 
cell which acts as a simple osmometer. It will then be possible to — 
judge more accurately the value of the data furnished by the many 
methods based upon the study of the osmotic relations of living 
cells. Such a typical cell may be pictured as a body of solution sut- : 
rounded by an elastic membrane permeable to and bathed by the 
solvent (in this case water), and ‘slightly if at all permeable to the : y 
_ contained solute. Water will enter such a cell until the internal i 
hydrostatic pressure produced by the tension of the stretched 
owe 
thus ¢ arise a condition of : quilibriun a which b will be main- : eS 
water to enter er the cell. ve 
