386 General Notes. | May, 
during the year 1881, are important as throwing light upon the 
nature of plant evaporation, and its dependence upon light and 
heat. Dehérain’s experiments (Chimie Agricole, p. 175) appear 
to indicate that the evaporation of water by the leaves of plants 
takes place almost as freely in a saturated atmosphere as in the open 
air, evaporation being regarded as a strictly vital process. As the 
accuracy of Dehérain’s results depend upon the perfect saturation 
of the air in his experiments, some careful experiments 
mometers indicating 84° F. During the experiment the temper- 
ature gradually rose from 73° F, (dry) to 8414° F. at 4.20 P. M., 
the two thermometers differing then but half a degree. At 5.10 
Pp, M, the temperature dropped half a degree, when complete 
saturation was for the first time reached. These observations 
show that perfect saturation is obtained with considerable diffi- 
culty, as the experiments upon leaves are ordinarily performed, 
and they indicate that it is desirable to carefully review the whole 
question of plant evaporation. 
S one step in this review, the following experiments were 
made to determine the nature of the influence of light and heat 
upon evaporation from leaves. A glass bottle with two openings 
was filled with water, the temperature of which was varied to sult 
the requirements of the experiment, and to keep the temperature 
more nearly constant this bottle was set into another glass Jat 
filled with water having the same temperature. A thermometer 
was placed in one of the openings, and through the other a six 
inch test-tube was thrust up to its top. Into this test-tube a cork 
was fitted, which was covered with tinfoil to prevent its absorbing 
moisture. This was the weighing cork, and had a loop ° 
platinum wire attached to it, by means of which the whole could 
be hung upon the hook of the weighing scales. Another cork was 
similarly prepared, and then split open and a healthy leaf of Orchard 
Grass (Dactylis glomerata) placed carefully between the two halves- 
By means of tinfoil and putty the cork was rendered imperee 
to moisture, while not interfering with the healthy and norma 
action of the leaf, which was still attached to the plant. ee 
The test-tube, with a small thermometer in it, and the weigh 
cork in place, was then accurately weighed and put into one of the 
