398 True. — On the Influence of Sudden Changes of 
under different circumstances apparently different results. If 
the lower extreme be near the zero point, and the intervening 
number of degrees be sufficient (i8°C. usually in the above 
experiments), a shortening of the radicle is generally seen to 
take place within five minutes. If the lower extreme, how- 
ever, be at a medium temperature (i8°) and the fall of tempera- 
ture be but 12° C., no such shortening is seen. Instead, 
however, an immediate retardation of growth invariably takes 
place. A change in the reverse direction gives an immediate 
elongation or an increased rate of apparent growth. Roughly 
speaking, the greater the number of degrees of temperature 
increase, the greater is the elongation. This statement is made 
only for temperatures used in these experiments. 
That the location of the minimum point, as such, has no 
decided influence, is shown by a computation from the 
averages drawn from the above experiments, and from others 
not detailed in this paper. The average elongation in the 
first fifteen minutes following the transfer from 0-40 to 19.0 0 C. 
is found to be 0-18 mm. or 001 mm. per degree. The corre- 
sponding elongation following the transfer from 18-0° C. to 
30° C. is 0-095 mm. or 0.009 mm - P er degree. The elonga- 
tion was obtained by subtracting the number of units of 
growth made during the fifteen minutes’ period preceding the 
transfer, from the number of units of apparent growth made 
during the like period following the change. The absolute 
elongation due to the change of temperature seems, therefore, 
within the limits here given, to vary according to the number 
of degrees intervening. 
Whether the maximum-temperature limit, as such, has any 
peculiar influence, does not appear from experiments here 
made. There seems to be no reason to expect such. 
With these conclusions may be compared the results of 
G. Kraus’ 1 experiments on tissues of internodes. Judging 
from the elongation and the contraction of isolated tissues, he 
found the tensions to change but slightly by variations of 
1 G. Kraus, Bot. Zeit. 1867, p. 124. Compare al^o Pfeffer, Zur Kenntniss der 
Plasmahaut und der Vacuolen, &c. Leipzig, 1890, p. 309 (163). 
