THE EVOLUTION OF HEAT BY AEROBES 373 



Other aroids may show differences, and the fact that the maximum temperature is 

 not attained in all parts at the same time makes certain divergences in the observa- 

 tions of different workers comprehensible. 



A rise of temperature of 5 or even of 10 C. has been observed in open 

 air on the inflorescences of a few Cycads l and Palms 2 , as well as in the 

 flowers of Nelumbo nucifera 3 and Victoria regia 4 . This applies more 

 especially to the stamens in the latter case, which in general appear to 

 become warmer than the carpels. Thus Saussure 5 observed a rise of tem- 

 perature of from 4 to 5 C. in the male flowers of Cucurbita, but of only 

 3C. in the female ones. In open slender flowers and inflorescences the 

 rise of temperature is usually trifling, but is often more pronounced than 

 in the foliage-leaves. Flowers commonly respire relatively more actively 

 than foliage-leaves, and at the period of opening both the respiration and 

 the production of heat increase 6 . 



Vegetative organs rarely show any pronounced production of heat. 

 Thus Dutrochet 7 observed a maximal rise of temperature of 0-34 C. (shoots 

 of Euphorbia lathyris) under the most favourable conditions, while the 

 rise was usually below o-iC. In many shoots, rhizomes, ripe fruits, and 

 other organs, no rise of temperature at all could be directly detected 8 . The 

 fact that when heaped together all plant organs show a rise of temperature 

 shows that all living parts are able to produce heat. When transpiration 

 was allowed Dutrochet often observed a fall of temperature of 05 C. below 

 that of the surrounding air, while when the shoot was killed the fall was 

 at first still more pronounced, owing to the fact that the immediate effect 

 of death upon a suddenly-killed turgid organ is to hasten the rate of 

 transpiration. 



In aerobes almost the whole of the heat is derived from aerobic 



1 G. Kraus, Abhandl. der naturf. Ges. zu Halle, 1896, p. 218. The earlier observations are 

 quoted here. 



3 G. Kraus, 1. c., 1896, p. 251. 



3 K. Miyake, Physiological observations on Nelumbo nucifera^ 1898, p. 18 (reprint from the 

 Botanical Magazine, Tokyo, Vol. xn). 



* Caspary, Flora, 1856, p. 218; E. Knoch, Bibliotheca botanica, 1899, Heft Ixxvii, p. 44. 

 Bory de St. Vincent (Journal de physique, 1804, p. 289) states that the flowers of Pandanus utilis 

 and of Cannaceae become in some cases warm enough to melt cocoa-butter. 



5 Saussure, Ann. de chim. et de phys., 1822, Bd. xxi, p. 296. The temperature of these and 

 other flowers was measured by a kind of air-thermometer. A few observations on the flowers of 

 Cactus and Pancratium are given by C. H. Schulz, Die Natur d. lebendigen Pflanze, 1828, p. 185. 



* Dutrochet (1. c., 1840, p. 81) observed a rise of temperature when the thermo-electric needle 

 was plunged in the ovary of the Rose, Papaver somniferum and Paeonia officinalis, when flower- 

 buds were examined in saturated air. 



7 Dutrochet, Ann. d. sci. nat., 1840, 2 e ser., T. xni, p. 44. Dutrochet and MacNab (Bot. Ztg., 

 l8 73> P- S^o) give observations on Agaricus, Boletus ; and Lycoperdon. 



* A slight rise of temperature was observed in tubers by Seignette, Rev.ge"n. de Bot., 1889, T. I, 

 P- 573- See also Dixon, Trans, of the Irish Academy, 1903, Vol. xxxil, iii, p. 145. 



