CHAP, ii.] of Plants. De Saussure. 57
for the view that heat in plants is simply a result of their respi- ration, as it is in animals. It is not necessary to describe at length the experiments which were made on heat in plants before 1822 ; they were one and all vitiated by a want of clear- ness in the statement of the question, which made success impossible ; it was assumed that this heat by raising the tem- perature of the plant would make itself felt by surrounding objects, and it was sought for exactly where it is least to be found, in the wood, in fruits and tubers, and generally in resting, inactive parts. Moreover the previous experiments, collected in Goeppert's book 'Ueber dieWarmeentwicklung der Pflanzen,' 1830, were so unskilfully managed that they could not possibly lead to any result. Nor could the question whether plants really develope internal heat, as animals do, be determined by a few cases of active development of heat in flowers, because an idea was prevalent at the time in connection with the theory of a vital force, that flowers as the organs of reproduction alone possessed the power of generating heat.
Lavoisier had clearly perceived in 1777 that the combustion of substances containing carbon by inhaled oxygen was the source of animal heat, and had proved it by experiments. Senebier, who first observed the rise of temperature in the in- florescence of Arum by the thermometer, had at least suggested in his work on physiology of 1800 (iii. p. 315) that a vigorous absorption of oxygen might be the cause of the phenomenon. Bory de St. Vincent reported in 1804 that Hubert, the owner of a plantation in Madagascar, had observed among other things that the air in which the flowering spike of one of the Aroideae had developed its heat could support neither animal respiration nor combustion. These indications were however disregarded, until de Saussure in 1822 proved directly the connection between the absorption of oxygen and the rise of temperature in flowers. It was however a long time before heat in plants was con- ceived of as a general fact necessarily connected with then respiration. This conception would have swept away the