Walter Stiles 
244 
experiments with seeds of Xanthium pennsylvanicum and small 
Scotch yellow split pea, the values for Q 1q between 5 0 and 35 0 C. found 
for Xanthium being 1-55 in one case, and 1-83 in another, and for 
pea i*6. Very similar, though on the whole lower values, were 
obtained by Denny (1917 a) for the temperature coefficient of the 
rate of passage of water through the detached seed coat of Arachis 
hypogaea (1-34 to 1*64). 
Brown and Tinker (1916 a) regard the rate of entry of water into 
barley grains as given by the equation 
or, integrating. 
dy 
di 
= k (a— y), 
log 
a 
a-y 
where y is the quantity of water absorbed in a time t, and a and k 
are constants. Shull, however, holds that both his own experimental 
results and those of Brown and Worley are better expressed by the 
equation 
y = «logj 0 (bt + I) + C, 
where y is the quantity of water absorbed, t the time of immersion 
and a, b and c are constants. For the whole course of water intake 
the time-absorption curves can, in some cases at any rate, best be 
represented by three such equations representing the early, middle 
and late stage of water absorption. Apart from their value in 
enabling the temperature coefficients to be calculated with exacti¬ 
tude, these equations do not help us much in explaining the processes 
of water intake. 
In the case of seeds, where the percentage of water is com¬ 
paratively low and the percentage of colloidal substances susceptible 
to imbibitional swelling very high, it is clearly impossible to describe 
the temperature coefficient of water absorption as a temperature 
coefficient of the cell membranes. To determine the effect of tem¬ 
perature on the different processes involved in the water intake by 
seeds, further experimental work is necessary. Denny’s work with 
seed coats separated from the seeds suggests a way in which this 
might be attempted. Sufficient data are, however, at present 
lacking. 
