400 True —On the Influence of Sudden Changes of 
magnitude to fully account for the transitory changes of 
length under consideration. 
That the change of turgor-pressure finds in the radicle 
observed an unmodified expression is hardly to be expected. 
The conditions of growth prevailing at the time of a change 
of temperature seem to modify the extent of the elongation 
and of the contraction, or, in case no contraction is seen, of 
the following growth-rate, in much the same way as is noted 
above (p. 383). The resolution of the resultants into their 
factors is a problem hardly soluble from the data at hand. 
That the sudden temperature-changes may act as stimuli 
which release growth influencing factors seems not unlikely. 
If such factors enter, their magnitude is a matter of uncer- 
tainty. It seems, in view of these possibilities, justified to 
regard the changes of length under discussion as due to varia- 
tions of turgor-pressure modified to a greater or less extent 
by factors having their origin in the organisms. 
It remains to notice the period of depression of growth 
seen to follow changes of temperature. As has been pointed 
out in connexion with the individual experiments, this depres- 
sion varies in duration with the different conditions offered. 
Plainly a transfer from 20-0° to i-o° C. can be followed by no 
recovery, since, at the lower temperature, activity is practically 
suspended. A transfer in the reverse direction, however, is 
usually followed by a more or less marked depression of 
growth. This depression-period may vary in length from 
a few minutes to days, and, as has been seen in cases, the 
normal growth may not be regained. 
The duration of this phenomenon depends (1) on the location 
of the lower temperature-limit to which the objects are exposed, 
and (2) on the duration of this exposure. 
In a general way, it may be said that the lower the tem- 
perature-limit lies, the shorter the exposure sufficient to 
produce a depressed growth upon the return to the higher 
temperature. By shortening the period of exposure suffi- 
ciently, the depression may be so far reduced that its presence 
is not to be detected. Otherwise stated, a certain minimum 
