176 THE HEAT OF PLANTS. 



In different races, the mechanism by which these variations of atmos- 

 pheric temperature are balanced acts with different degrees of perfection, 

 d hot ^ n ^ s a subdivision has been founded, and animals classi- 

 Mooded ani- fied as the cold and hot blooded. We are not, however, to 

 mals - attach much importance to such an arrangement : it is rather 



imaginary than founded on any real distinction. In man, the tempera- 

 ture is near 100 ; in fishes, it is about that of the water in w^hich they 

 live. Insects, in their larva and pupa condition, are cold-blooded; in 

 their perfect condition, hot. 



We have now to explain what physical principles are resorted to in 

 solving the problem of maintaining an organic form at a constant tem- 

 perature in a medium the heat of which is variable ; and as we may 

 reasonably anticipate that these principles are the same in every tribe of 

 life, it will facilitate our investigations to commence with the simplest 

 cases first. 



There are two periods in the life of a plant during which it simulates 

 Two periods of the functions of an animal in ^maintaining a temperature 

 heat in plants, higher than that of the surrounding air. These periods are, 

 1st, at the germination of the seed ; 2d, during the functional activity of 

 the flower. 



If a mass of seeds be laid together, as in the making of malt, the op- 

 Heat of germ- eration being conducted at a gentle temperature, and with the 

 ination. access of atmospheric air, oxygen disappears, carbonic acid is 



set free, and the temperature rises forty or fifty degrees. A process of 

 oxidation must therefore have been carried into effect, and to it we trace 

 the heat disengaged, for carbon can not produce carbonic acid without a 

 rise of temperature ensuing. The loss of weight which a seed exhibits 

 is therefore due to its loss of carbon, and the whole effect is explained in 

 the statement that atmospheric oxygen has united with a portion of car- 

 bon contained in the seed, producing carbonic acid gas and an evolution 

 of heat. 



Again, during flowering, the same action is repeated. The flower re- 

 Heat of inflo- moves from the surrounding air a portion of the oxygen it 

 rescence. contains, and replaces it with carbonic acid, the temperature 

 rising, as accurate experiments have proved, in absolute correspondence 

 with the quantity of oxygen consumed. Nor is this elevation insignifi- 

 cant. A mass of flowers has been observed to raise the thermometer from 

 66 to 121. 



If thus the disengagement of warmth is the result of oxidation, it must 

 Oxidation the depend on the presence of air, and be regulated by the rapidity 

 e^vation^of 6 wit ^ which oxygen can be supplied. As we pass from the 

 temperature, consideration of plants to that of animals, we discover that the 

 production of heat must be connected with the power and precision with 



