394 True . — On the Influence of Sudden Changes of 
during the remainder of the experiment. This rate, however, 
is but about two-thirds as great as that seen in this tempera- 
ture at the beginning of the experiment. 
For comparison with the above is given in Table XIX 
the result of a somewhat similar experiment with a root of 
Pisum sativum. 
The prolonged contraction here following the transfer to 
the lower temperature was seldom seen. The return of the 
normal growth here takes place in a gradual manner. 
In Table XX is shown the record made by a radicle of 
Litpinus albus exposed for 30 minutes to a temperature of 
o- 5 ° C. 
TABLE XX. 
Period. 
Growth. 
Temperature. 
3-30-4 
1 1 -5 units 
i9-2°C. 
4 - 4-30 
-0-5 „ 
o-5 „ 
4-30-5 
11 *5 „ 
19-3 „ 
5-5-30 
io-o „ 
20-0 ,, 
1 unit = 0-0182 mm. 
The rate of elongation following the return to the usual 
temperature is equal to the growth-rate prevailing before the 
exposure. 
In the experiments thus far considered, we find that a mini- 
mum period of exposure to a low temperature exists, following 
which no reaction can be detected with the scale ; we find 
also in experiments involving microscopic measurements that 
the retardation or reaction may be reduced by decreasing the 
period of exposure to the low temperature. A certain duration 
of the application of the stimulus is necessary to call forth 
a plain reaction. 
In the preceding experiments, the lower temperature limit 
was near the minimum for growth. Those following deal 
with the effects arising from changes between limits that are 
plainly useful for plant-growth. 
