35 
Heat by Wounded Plants . 
with the exception of a few cases where the wound gaped so 
widely that it was impossible ; under which circumstances the 
needle was stuck into the tissue directly behind the cut. Why 
this latter was not always done will be explained in a fol- 
lowing paragraph. It is unfortunately impossible to obtain 
the necessary comparison of temperature between the injured 
and uninjured parts without inserting the needle into the 
latter as well as the former, and thereby wounding it slightly. 
The wound is slight, however, and as oxygen of the air can 
scarcely gain access around the needle thus introduced, the 
difference is not so important as it would seem. The error, 
too, if any, would tend to counteract the effect of the intended 
wound in the injured part, and hence in a qualitative deter- 
mination such as this is not serious, especially since all the 
objects experimented with were treated in the same manner. 
In order to ensure absolute certainty that the injury purposely 
inflicted would not influence both needle-points, two objects 
were used (e.g. two potatoes) which are here always referred 
to as the uninjured and injured objects. It was found by 
repeated experiments that the various plants used, if they 
were of the same age and had presumably been kept under 
the same conditions, never varied appreciably in temperature 
in the uninjured condition. Without going further into the 
description of the manipulations gone through, it is sufficient 
to repeat that the various objects investigated were treated in 
as nearly as might be the same manner, and any errors 
arising thereby largely equalized ; which it will be appreciated 
is the most important desideratum in a purely qualitative 
determination. The writer recognizes, of course, that in 
a quantitative estimation of the amount of heat produced a 
much finer degree of accuracy would be required, such as 
Rodewald 1 employed in his admirable researches. 
As a control for the thermo-electric method, a series of 
experiments were carried on with a simple form of a calori- 
meter, by which the temperature-curve of a mass of plants 
could be determined. The results were of a confirmatory 
1 Prings. Jahrb., 1. c. 
D 2 
