Walter Stiles 
234 
of (1) effects attributable to purely osmotic relations of the cell, 
(2) effects due to the entrance or exosmosis of dissolved substances 
which alter the osmotic relations, (3) effects on the capacity for 
imbibitional swelling of cell wall, protoplasm and vacuole, and 
(4) effects resulting from any influence on the permeability of the 
cell wall and protoplasm. It may not always be possible to dis¬ 
tinguish with certainty which of these various effects is or are mainly 
responsible for observed behaviour. It will therefore be most satis¬ 
factory first to describe the results obtained experimentally, and 
then to discuss how far these observed results are to be correlated 
with protoplasmic permeability or with other phenomena indicated 
above. 
Temperature 
A number of earlier observations have suggested that the rate of 
intake of water by, or its excretion from, plant cells and tissues, is 
considerably influenced by temperature. Among these may be men¬ 
tioned those of Vesque (1877) on the absorption of water by forest 
trees, Wieler (1893) on the bleeding of cut stems of a number of 
plants, and Lepeschkin (1906) on the exudation of water by the 
sporangiophores of Pilobolus. As these results, suggestive as they 
are, do not provide us with exact data for our analysis, we may 
pass at once to a consideration of those researches in which exact 
measurements of the effect of temperature on water intake or excre¬ 
tion have been attempted. 
Determinations by the Plasmolytic Method 
Systematic attempts to determine the influence of temperature 
on the rate of passage of water through the cell membranes were 
made by Krabbe (1896) and van Rysselberghe (1901). The former 
measured the time required for complete contraction of cylinders of 
turgid pith when plasmolysed at different temperatures and con¬ 
cluded that the rate of excretion and absorption of water rises with 
increase of temperature. 
Van Rysselberghe used cylinders of elder pith, epidermal cells of 
Tradescantia and Begonia, Lenina, Spirogyra and other plants. The 
cylinders of pith were plasmolysed at different temperatures in 
strong sucrose solutions (0731 M) and the amount of shrinkage 
measured at different times over a period of 24 hours. The tempera¬ 
ture effect was determined by comparing the amount of shrinkage 
after two hours at the different temperatures. But obviously this 
