Turgor and of Temperature on Growth . 391 
by shortening the period of exposure to the low temperature, 
the change to the higher degree was followed by no retarda- 
tion that could be detected by measurements with the scale ; 
the normal growth seemed to be immediately assumed. 
It was noticed in comparative experiments with roots culti- 
vated in sawdust, that a somewhat longer period of exposure 
to the cold was necessary in order to produce a retardation 
than in cultures in water. A recovery of the normal growth 
took place more rapidly in the former case. 
In order to study more accurately the results following 
temperature-changes, the horizontal microscope was again 
brought into use. Plainly this method of measurement is 
suited only to experiments occupying shorter periods of time, 
TABLE XVI. 
Period. 
Growth in scale units. 
Temperature. 
IO.IO-IO.40 
16-0 units 
i8- 5 °C. 
IO.40-JI.IO 
5-o „ 
18.6 „ 
II. IO-II.4O 
2-0 „ 
06 
II.4O-3.IO 
2-0 units per | hr. 
18-8-19-7 » 
3.IO-3.40 
3-o n 
19*7 » 
3.40-4.IO 
2-5 „ 
19.8 „ 
4.IO-4.40 
2-5 „ 
19.8 „ 
4.40-6.IO 
2-0 „ 
19-8-20-0 ,, 
i unit = 0-0182 mm. 
and is, therefore, not well adapted to the study of long-con- 
tinued reactions following prolonged exposure to low tem- 
peratures. Only those phenomena which occur soon after 
a change can be here most profitably followed. When the 
exposure to low temperatures is short, and the normal growth 
soon returns, this instrument is also called into use. 
Before passing to the latter class of experiments, we will 
briefly notice the results seen to immediately follow the return 
to a higher temperature after a prolonged exposure to cold. 
In Table XVI is shown the record of a Vida Faba radicle 
