Turgor and of Temperature on Growth. 383 
The study of these elastic changes of length was made 
under differing conditions, and the essential features were 
found not to vary from the foregoing. The contraction ob- 
served to accompany the transfer to the KN0 3 solution was 
always of less magnitude than the elongation seen to follow 
the return to water. 
It must not be forgotten that in each case we have to do 
with more than a simple turgor-change. The growth pre- 
vailing at the time of such change of medium enters as 
a complicating factor. If we transfer a root from water 
to a saltpetre solution, we cannot regard the growth-rate as 
instantaneously adjusting itself to the new medium. The 
former speed gives a certain impulse that must be overcome 
before the new conditions can produce their characteristic 
effect. It will still operate for a short time in the new 
medium. We would not expect, therefore, the entire work 
resulting from the change of turgor to find expression in the 
altered length of the root, a part being expended in working 
against the prevailing impetus of growth. We see as a con- 
traction only the resultant of the two factors, the larger of 
which is the elastic change due to turgor. 
In the case of the transfer from the saltpetre solution to 
water, we have the same two factors present, but here they 
work in the same direction, and the alteration in length is 
equal to the sum of the two factors. The contraction is the 
sudden halt called forth by the substratum, the elastic elonga- 
tion is the push given by it. To resolve the resultants above 
found into their numerical components is here not attempted. 
As may be seen in the experiments above detailed, a transfer 
from water to a saltpetre solution is followed by a more or 
less prolonged period of retarded growth \ A reduced 
growth-rate is likewise seen to follow very regularly the 
reverse change of medium, although a quite rapid rate of 
growth may prevail in the KNO s solution immediately 
prior to the transfer to water. Thus a depression of growth 
1 In Tables II to VII, all radicles were placed in water and allowed to assume 
a normal growth-rate before being brought into the KN0 3 solution. 
E e 2 
