52 SILOS, ENSILAGE AKD SILAGE. 



heat from evaporation. Under special conditions, where 

 the loss from evaporation is reduced to a minimum, and 

 the plants are massed in an atmosphere saturated with 

 moisture,* the heat evolved becomes sensible and is 

 readily detected. 



In the malting of barley a temperature of 110 has 

 been observed, and this, too, under conditions that were 

 not the best to prevent the loss of heat from evaporation 

 and radiation ; and a thermometer placed in the center 

 of twelve spadixes of Arum Cordifolium showed a tem- 

 perature of 121 when the external air was only 66. f 

 The heat evolved by these flowers was greatest when the 

 plants were freely exposed to the air and the exhalation 

 of carbonic acid was most active. On the other hand, 

 Dutrochet J found that the evolution of heat in green 

 growing plants, as in the young twigs and leaves, was 

 subject to a diurnal variation, and that it was most 

 active in the middle of the day, when the absorption of 

 carbonic acid and the exhalation of oxygen was going on 

 with the greatest rapidity. From these statements it 

 appears that heat is most rapidly developed when the 

 metabolism of plant cells is most active, and this is 

 indicated by the maximum absorption of carbonic acid 

 in the green parts, like the leaves, and the maximum 

 exhalation of carbonic acid, in special organs, as the 

 flowers and fruits, in which chlorophyll is not perform- 

 ing its special role of fixing the carbon of carbonic acid. 



The living cells of various tissues may also, as pointed 

 out by Pasteur, perform the function of the true, or 

 organized ferments, in producing alcohol, lactic acid, 

 etc.. but this function is but an incident of their meta- 



* Tyndall's experiments on radiant heat show that pure dry air is transparent 

 to heat (i. e., is not readily heated), but that moist air absorbs heat, and is, there- 

 fore, readily warmed. When air is nearly saturated with the vapor of water, the 

 absorption of heat is ninety times greater than in dry air. Tyndall on Heat, pp. 

 398 399, etc. 



t Carpenter's Comp. Phys., pp. 451-452. 



JAnn. des Sci. Nat., 2d. series, XII, p. 277. Carpenter's Comp. Phys., p. 451. 

 Dalton's Human Phys., pp. 240-244. 



