42 Richards . — The Evolution of 
temperature-curves with the thermo-electric apparatus (Expts. 
13, 14, 20), but were not tried with the bell-glasses. 
Leaves afforded an entirely different type of tissue. Or- 
dinarily speaking these are not well adapted for the use of 
a thermo-element. The thick leaves of Aloe were experi- 
mented with in this way, although without success ; but with 
onion-bulbs very interesting results, of which more will be 
said later, were obtained. With the bell-glasses ordinary 
leaves could be employed: experiments with those of Lirio- 
dendron and Dier villa gave very satisfactory results (Expts. 
24, 25). The maximum, as would be expected, was reached 
much more rapidly than with massive tissues. In four and 
a half hours the injured leaves, in the case of Liriodendron , 
were 0-75° C. warmer than the uninjured, the latter showing 
an average temperature of about 0-4° C. over that of the air. 
By the next day there was little difference, and that speedily 
diminished as the injured leaves died. 
Of all the plants investigated onion-bulbs gave a far stronger 
reaction than any other. With the bell-glasses the average 
maximum of two experiments (Expts. 26 and 28) was 3*3° C. 
This high temperature continued for some time ; and it was 
not until the fifth day that it sank again to the normal plus 
temperature of about 0-5° C. In one experiment (Expt. 27) 
it will be noticed that the maximum was much lower ; but, 
at the same time, the temperature of these onions in the 
uninjured state was very much higher than in the other two 
experiments, being 1-2° C. above air-temperature. This 
accounts for the low maximum in the injured condition, 
and is probably to be explained by a difference in metabolic 
activity of the onions. It may be mentioned that the onions 
used in this experiment did not come from the same source 
as the others. With the thermo-element, however (Expts. 17 
and 19), no remarkably high temperature was detected in 
the cut, or rather immediately behind it ; since in onions the 
wounds gape so that it is impossible to stick the needle 
advantageously into the cut itself. This fact was puzzling 
until, by subsequent experiment, it was found that the whole 
