388 True, — On the Influence of Sudden Changes of 
weak stimuli in inducing leaf-movements of Oxalis Acetosella 
and of Mimosa pudica 1 . 
Materials and Methods. 
As far as here applicable, the materials and methods used 
were like those already described in the first part of this paper. 
Radicles of the same species were germinated in the same 
manner. Measurements were made with the scale and the 
horizontal microscope. Owing to the liability of disturbance 
by the expansion and contraction of parts of the apparatus, 
the measurements with the horizontal microscope were usually 
made from point to point. The results thus obtained differed, 
however, but very slightly from those yielded by the measure- 
ment of the movement of the tip on the ocular micrometer. 
To obtain the desired temperatures, resort was had to 
a number of devices. As the experiments demanding low 
temperatures were made in winter, it was found easy, by the 
use of a cold room and ice, to obtain the desired result. The 
higher temperatures were found in rooms provided with auto- 
matic heat-regulators. For the limited time occupied by the 
experiments involving the use of the horizontal microscope, it 
was found practicable, with a room-temperature of 19 0 C. to 
obtain the desired temperatures by the use of a microburner 
or of small pieces of ice added at regular intervals. 
Because of the obvious advantages, experiments were usually 
made with roots in water. Comparison experiments were 
made in sawdust. 
Experimental. 
In order to gain a general view of the effects accompanying 
extreme changes, several series of roots of Vicia Faba were 
exposed to a temperature near the zero point for various 
periods of time, and were then suddenly brought into a tem- 
perature of about 24° C. 
Four roots of Vicia Faba seedlings were exposed for 220 
hours to a temperature varying between 0-40 and 2*5° C., 
1 Pfeffer, Pflanzenphysiologie, 1881, Bd. II, p. 231. 
