50 DUBLIN UNIVERSITY 



In the growth of fungi, too, the process is one of oxygination. Payen 

 lias found products of ammonia, oxygen, carbonic acid, water, and sugar; 

 and heat has been proved to have been given out in their growth. In 

 the fructification of many plants, the temperature has exhibited a very 

 marked increase : thus, Hubert and Bory de "Vincent have observed, es- 

 pecially in the spathe of the Arum cordifolium, during fructification, a 

 rise of 34°; here, too, oxygen was being combined so as to form car- 

 bonic acid ; for in the formula of the essential oils then developed, a larger 

 amount of carbon and hydrogen was required, than furnished by cellu- 

 lose. But such are not the questions on which I wish to engage the 

 attention of the meeting, but one, I think, of a higher physiological im- 

 port, — whether, consequent on the action perpetually going on during 

 vegetable growth, while cellulose, woody fibre, &c, are being formed, 

 is there a change of temperature ? — and, if so, can we at all come at a 

 proximate determination as to its amount? If such a cause of change 

 of temperature exists, we must be prepared to find it marked to a great 

 extent by evaporation, radiation, and the shifting of the fluids of plants; 

 and although, at first sight, it might be supposed to be an easy matter to 

 determine this question, and the simple introduction of a thermometer 

 or thermo-electric needle into the growing tissues might be imagined to 

 be all that would be necessary to prove the truth of the result ; yet so 

 many disturbing accidents interfere with these experiments, as to fully 

 account for the results of the best observers on this subject — some record- 

 ing positive, some negative answers, to the question. Evaporation has 

 generally got all the credit of the low sensible temperature of plants, 

 and this has followed, I think, too hastily from the experiments of 

 Hales and others ; but in certain particular growths this cannot ac- 

 count for the observed low temperature. In certain melo-cacti little or 

 no evaporation can take place from their globular surface, no cooling in- 

 fluence from their parched and scanty resting place ; and yet we are told 

 that they contain a fluid, always cooler than the surrounding air or soil. 

 In those luscious fruits of the tropics, how cool are they ! much cooler 

 than any other portion of the plant ; and, surely, they can be subject to 

 little evaporation from their surface : besides, I doubt much if, on the 

 whole, absorption does not balance evaporation in vegetable life. "We 

 know how arid are those portions of the land divested of vegetation; and 

 in those districts denuded of their forests, the rivers have decreased in 

 volume. In our own country, are there not many traces of large rivers, 



