£Q2 BOTANICAL GAZETTE [FEBRUARY | 
LIGHT AND DARKNESS. 
I made a considerable number of experiments on the diurnal 
opening and closing of the stomata, using as a control either a 
leaf whose stomata remain open at night, or an artificial leaf 
made of damp linen, or a withered leaf. The curves obtained 
show clearly enough a lowering of the temperature at sunrise, 
and arise at sunset, but I have gradually come to think the 
results not sufficiently trustworthy to be published, and for the 
present I withhold them. 
ARTIFICIAL CHANGES IN ILLUMINATION. 
The most interesting results were obtained by artificial dark- 
ness. In my early experiments the plan followed was to fix 4 
large horizontal sheet of glass close above the bulbs of the 
recorder which were placed as near as possible to each other. 
By covering the glass with black cloth, a considerable diminution 
in illumination could be produced without any danger of altering 
the hygroscopic conditions of the air. 
Afterwards I managed to produce a greater degree of dark- 
ness by adding a curtain, hanging down like a flounce, all round 
the glass plate. As long as the horizontal glass was uncovered 
the leaf on the recorder bulb was well-illuminated, as the experi- 
ments were made in a greenhouse. When the black cloth 
was drawn over the horizontal glass the light was sufficiently 
diminished to produce rapid closure of the stomata; at the same 
time the other physical conditions are not altered in such a way 
as to produce a difference in temperature between the two bulbs. 
In order to make sure that the increase in the leaf temperature 
(which occurs in darkness) is actually due to stomatal closure 
and not to purely physical effects, several experiments were 
made with ‘‘artificial leaves.” The two bulbs, wet and dry, 
were placed close together under the flounced glass plate, one 
bulb being covered with damp linen, the other being left naked, 
or covered with dry paper on platinum. The effect of alternat- 
ing periods of light and darkness on the relative temperature 
was uncertain and variable, and in this respect very different 
from the results obtained with living leaves. 
Ae The results with 
artificial leaves were as follows: 
