The Temperature Relations of Foliage Leaves. 79 
objects. Twenty-five awns of barley were first taken and bound in 
a bundle. These ignited in three to four seconds. A single awn 
remained unburnt for over four minutes. Similar results were 
obtained with fresh shoots of Asparagus plumosus. A single 
phylloclade remained unburnt for five minutes, while a shoot with 
several phylloclades together ignited immediately. Like results 
followed from comparison under similar conditions of a large 
phyllode of Acacia and a small leaf of Erica, the phyllode burning in 
nine seconds, the leaf taking forty to fifty seconds. 
Wiesner ascribes this difference by which small parts remain 
lower in temperature, not to a difference in the excess of absorptive 
power for heat over loss of heat by radiation, but to the much 
greater conduction of heat from the relatively large surface of the 
small parts, combined with the greater diathermancy caused by 
their thin texture. 
As supporting this opinion he describes parallel experiments 
carried out both with Acacia phyllodes and with Erica leaves, in 
which in each case the height of the sun was the same, the tem¬ 
peratures as registered by a black bulb thermometer were equal, but 
the air-temperature was considerably lower in one case than the 
other. This caused a very much longer time to elapse before 
ignition, since now the loss of heat from the surface to the 
surrounding air at a low temperature was much greater. Thus 
small dimensions or fine division of plant-parts prevent a high 
internal temperature from being attained. 
Passing from the environment as conditioning temperature in 
leaves to the subject of the effect of the activity of the leaf itself on 
its temperature we note that Molisch has been able to show that a 
rise of temperature due to respiration can be clearly shown in the 
case of the leaves of many species. He gathered large quantities 
of leaves, taking care that they should be dry, and placed them in a 
wicker basket. This was put inside a wooden box, the intervening 
space being packed with shavings. The whole was surrounded by 
several layers of cloth and the top covered by pasteboard through 
which a thermometer was passed into the leaves. Quantities of 
from three to five kilogrammes of leaves were used in each experi¬ 
ment. The cover was taken off from time to time to examine for 
the presence of bacteria or fungi and to see if the leaves were still 
turgid or whether they were discoloured and dead. The experiments 
were carried on for several days, in one case for sixteen days, the 
temperature being read at first hourly, later three or four times a 
day. 
The curve of temperature readings thus obtained had two 
maxima with lower readings between, e.g., in Carpinus Betulus the 
temperature reached 5L5 n C after fifteen hours. It then sank to 34° 
after forty-eight hours. It attained its second maximum of 47° after 
104 hours and then gradually sank to 31° after 180 hours. This was 
a typical curve. By examination it was ascertained that at the first 
maximum the leaves were living and almost free from bacteria or 
fungi. The high temperature therefore was due to respiration. It 
killed the leaf and then the temperature began to fall. The second 
rise could clearly be attributed to the action of bacteria and fungi, 
as at its height the leaves were covered with these organisms. 
Leaves vary very much in the temperature they attain under these 
