212 FLOWERING AND ITS CONSEQUENCES. 



same quantity of vegetable matter by decay, a heat which is 

 employed by the gardener when he makes hot-beds of tan, decay- 

 ing leaves, and manure, or by the breathing of animals, where 

 it maintains their elevated temperature (364). The consumption 

 of a given amount of carbon and hydrogen, under whatever form, 

 and whether slowly or rapidly, generates in all cases the very same 

 amount of heat. Now, since flowers consume carbon and produce 

 carbonic acid, acting in this respect like animals, they ought to 

 evolve heat in proportion to that consumption. This, in fact, they 

 do. The evolution of heat in blossoming was first observed by 

 Lamarck, about seventy years ago, in the European Arum, which, 

 just as the flowers open, " grows hot," as Lamarck stated, " as if 

 it were about to burn." It was afterwards shown by Saussure in 

 a number of flowers, such as those of the Bignonia, Gourd, and 

 Tuberose, and the heat was shown to be in direct proportion to the 

 consumption of the oxygen of the air, or in other words, of the 

 carbon of the plant. The increase of temperature, in these cases, 

 was measured by common instruments. But now that thermo- 

 electric apparatus affords the means of measuring variations inap- 

 preciable by the most delicate thermometer, the heat generated by 

 an ordinary cluster of blossoms may be detected. The phenome- 

 non is most striking in the case of some large tropical Aroideous 

 plants, where an immense number of blossoms are crowded to- 

 gether and muffled by a kind of hood, or spathe (390), which con- 

 fines and reverberates the heat. In some of these, the temperature 

 rises at times to twenty or even fifty degrees (Fahrenheit) above 

 that of the surrounding air.* 



373. The source of the heat in flowering is therefore evident. 

 As to its object, we cannot say whether its production is the imme- 

 diate end in view, and the plant burns some of its carbon merely 



* This increase of temperature occurs daily from the time the flowers open 

 until they fade, but is most striking during the shedding of the pollen. At 

 night, the temperature falls nearly to that of the surrounding air; but in the 

 course of the morning the heat comes on, as it were, like a paroxysm of 'fever , 

 attaining the maximum, day after day, very nearly at the same hour of the 

 afternoon, and gradually declining towards evening. In ordinary cases, the 

 heat of flowering is absorbed by the vaporization of the sap and the exhala- 

 tion of oxygen by the foliage (besides, a large amount is absorbed from the 

 solar radiation and rendered latent in the process of assimilation) ; so that the 

 actual temperature of a leafy plant in summer is lower than that of the atmos- 

 phere. 



