296 BOTANICAL GAZETTE [CCTOBER 
much more readily than lactose; hence might arise the differ- 
ence between the effect of these two substances upon the 
organism. 
Considering these results, together with those heretofore 
published, theresseems little room for doubt that the response 
of this plant is brought about by a change in its relation to 
water. An increase in the osmotic pressure of the surrounding 
fluid must invariably extract water from the cell (since plant 
membranes are readily permeable to water), and a decrease of 
such pressure must cause the cell to take up more. However, 
an increase in the amount of sugar in the medium might influence 
the plant otherwise than im the way just mentioned. There 
might be, for instance, a chemical effect produced by the car- 
bohydrate molecules. Also, it is readily conceivable that an 
increase in the number of electrically charged ions in the medium 
might exert some specific influence upon the protoplasm aside 
from mere change of water relation. But it is hardly conceivable 
that any chemical influence exerted by sugar molecules could be 
identical in its effect with an influence exerted by electrolyte 
ions. Thus we are almost driven to the following conclusions: 
(1) since solutions of electrolytes and non-electrolytes affect 
the organism in the same way, they must exert a common influ- 
ence upon the cells; and (2) since it is inconceivable that there 
is any chemical influence common to the two forms of solution, 
the response must be due to the one factor which is common to both, 
namely, change in the water relation. Whether this change in 
the water content of the cells acts merely through the mechan- 
ical effects of a change in the turgor pressure of the cell sap, oF 
whether the response is brought about by a more subtle adjust- 
ment within the protoplasm itself, we have at present no means 
of telling. It seems probable that both these factors are opera- 
tive. 
It is of interest to note here that while the organism often 
dies in a mineral solution whose pressure is * and invariably 
dies in stronger mineral solutions, yet it lives indefinitely and 
apparently without injury in a normal sugar solution. This is 
