102 ANATOMY AND PHYSIOLOGY OF 



Ohserv. Tlie earlier expcrinients to determine tlie temperature of 

 plants, by sinking tliermometers in holes bored in tbe triinkb of trees, 

 were completely incapable of giving a decidre answer to the question 

 whether plants evolve a proper heat, since a number of ciicumstances, 

 the effect of which cannot be taken into account, are influential upon the 

 temperature of the tree, namely, the direct warming action of the rays 

 of the sun, the cooling influence of evaporation, the sometimes warm- 

 ing, sometimes cooling communication of the temperature of the soil, 

 through the medium of the ascending sap, which exercises an influence 

 according to the time of year, and the difference of depth to which the 

 roots penetrate, not to be accurately determined in isolated cases. Under 

 these circumstances, it is readily explicable that the experiments made by 

 different observers do not agree. While I^au found that the mean tem- 

 perature of the tree agreed with the mean temperature of the air, 

 Schubler found the tree 1^" to 2f ° colder than the air in summer, and 

 in spring, on the contrary (March, May), about ll** to 3° warmer. 

 While in the experiments of Schubler, made on pretty thick trees, the 

 temperature of the latter never attained the extreme of the temperature 

 of the atmosphere, Beaumur saw slender trees heated 18° to 29° above 

 the temperature of the aii', in the sun. Under these- circumstances, the 

 slight evolution of heat of single plants must vanish without leaving a 

 trace, in. the considerable, and, in some cases, discordant variations of 

 temperature, dependent on external influences. 



A very great evolution of heat occurs in the blossom of the 

 Aroidese. This is considerable even in our Arum maculafum, 

 and, according to Dutroehet^s researches (" Go')nptes rendus" 1839, 

 69 o), rises to 25" — 27° above the temperatnre of the air. But this 

 phenomenon is seen 7"^ far higher degree in Golocasia odora, in 

 wliicli plant it has been investigated by Brongniart (" Nouv, Ann. 

 d. Museum," in.), Vrolik and Vriese (" Ann, des Sc. Nat!' sec, ser, 

 V. 134), and Van Beet and Bersgma ("Obs, ihermo-eleet s. Velev. 

 de teonpcrat dee fleurs d, Oolocas. odor" 1 838). These last ob- 

 servers found the maximum of heat 129*", -when the temperature of 

 the air was 79°. The seat of the strongest evolution of heat 

 alters during the time of flowering ; namely, after the spathe has 

 opened, the antheis manifest the greatest heat ; they begin to 

 cool down with the emission of the pollen, after which the upper 

 part of the spadix, covered with abortive stamens, grows warm. 



Similar observations — ^not, however, made with the thermo- 

 meter, and therefore not fitted to give an accurate determination 

 of the heat given off by flowers — ^liave been made on Arum 

 italicum, A. Dracunculus, Galadmm viviparum, G pinnati- 

 fidum, and Galla cethiopica, by Sausa^ire, Goppert, Schultz, Tre- 

 viranus, Gartner, and others. 



The evolution of heat in the blossom of the Aroidese exhibits a 

 daily maximum and minimum, which, howevei^, it is remarkable, 

 that different observers found to occur at different times of the 

 day ; thus, in A, ^niaculatum, the maximum occurred in the 

 morning (Dutrochet), wliilst Senebier found it occur after six 



