Measurement of Rate of Shrinkage of Turgid Tissues. /. 287 
in position, was reduced to a minimum. That this was accomplished was 
evidenced by the fact that even the most flaccid tissues when left attached 
to the lever showed no sign of the slow creeping extension that an appre- 
ciable elongating strain must produce. 
Whilst very sensitive to any change in the length of the plant cylinder, 
the apparatus would give the same reading for many hours when a turgid 
piece was kept at constant temperature and freely supplied with water. In 
all the experiments, the freshly gathered material was kept in slowly 
running tap-water for some hours before use in order to ensure that the 
material was turgid. In ordinary cases one or two hours in water was 
sufficient for this purpose, but in very dry weather six hours or even more 
would be necessary. This previous immersion appeared to have no effect 
on subsequent treatment with sugar. When first placed on the apparatus 
distilled water was passed through the plant cylinder to see whether any 
further intake of water was occurring ; the sugar solution was only passed 
through when the length of tissue showed a practically constant reading 
with the distilled water. 
For an experiment at any temperature other than that of the laboratory 
the water-bath and chamber were previously adjusted so that the latter 
was at the desired temperature with distilled water flowing through the 
apparatus. Several trials were made beforehand, and it was found that, apart 
from variations in the temperature of the laboratory itself, the temperature 
of the water-bath had to be well above that desired in the chamber, e. g. 
from 3 0 at lower temperatures to 1 5 0 C. at highest temperatures. 
The control of the temperature was effected by (a) cooling or heating 
the water-bath, and (b) regulating the rate of flow of liquid through the 
apparatus. A temperature of 5 0 to 6° C. was produced in the chamber by 
packing the water- bath with ice and salt, and keeping melting ice in the 
chamber ; by this means a constant temperature could be maintained for 
hours. A temperature of 8° to ]o° C. was obtained by keeping the water- 
bath cool with ice and salt, but leaving the chamber to establish its own 
equilibrium. At high temperatures the water-bath was heated by means of 
a gas flame regulated by a thermostat, and the rate of flow of the two 
solutions to be used was carefully adjusted beforehand, so that at a known 
rate for each solution the temperature of the chamber would be maintained. 
The regulation of the flow of liquid was achieved by adjusting the pressure 
under which the liquid was driven through the apparatus, aided by the 
various taps, which could be turned partly off if necessary. The sup- 
plies of liquid were contained in ‘ aspirators ’ — Marriotte bottles — which 
give a constant flow of liquid ; so adjusting the height of the exit-tube, 
M, of the chamber determined the rate at which, other things being 
equal, the liquid would flow through the apparatus. With practice it 
became possible to keep the temperature of the chamber constant during 
