3i 
Heat by Wounded Plants. 
It should be understood at the outset that the results herein 
recorded should be taken as no more than a qualitative, and 
not as a quantitative, determination of the heat produced by 
injured plants. The object of the research was, in the first 
place, to establish the fact of a rise in temperature, if any, 
following the wounding of plant-tissues ; and in the second 
place to determine the curve of the change of temperature. 
While all possible pains were taken to shut out, in so far as 
could be, any sources of error, the extreme accuracy of 
Rodewald’s 1 quantitative research was not so necessary. 
As regards the apparatus and methods used, the thermo- 
electric element, in connexion with a mirror-galvanometer, 
was, as has already been hinted, mainly employed. The 
bolometric method was not used, since the former means 
proved sufficient for the purposes desired. A simple thermo- 
element similar to the form used by Dutrochet 2 , was the one 
selected. Such a single element is by no means so delicate 
as is a battery of twelve or thirty-six, such as Rodewald 3 
employed, but it proved sensitive enough, and was more 
advantageous, since the wound made by the element in the 
tissue under experimentation was reduced to a minimum. 
Such an element consists of two pieces of soft iron wire 
connected by a bow of German-silver wire, the points of 
contact being soldered by means of silver. The free ends 
of the iron wires are connected by means of binding screws 
to the wires from the galvanometer. The precise form of the 
points of this thermo-electric needle was only determined by 
experiment. At first sharp needle-points were tried, but 
proved ineffective for the purpose in hand, since they freed 
themselves too easily from the tissue in which they were 
imbedded. It was found that spatulate points, the idea of 
using which was obtained from Stahl 4 , were preferable, afford- 
ing as they do a firmer hold in the plant, and also a larger 
1 Pringsheim, Jahrb., Bande xviii, p. 263 ; xix, p. 221 ; xx, p. 261. 
2 Annales des Sciences Naturelles Bot., Tome xiii, Serie 3, p. 5 et seq. 
8 Prings. Jahrb., Band xviii, p. 276. 
4 Stahl, Ann. du Jardin Bot. de Buitenzorg, Vol. xiii, p. 153. 
