182 On Flowering, and its Results. 



back carbonic acid and water to the air, instead of taking 

 these materials from the air. It is in flowering that they 

 actually consume most. In fruiting, although the plant is rob- 

 bed of a large quantity of nourishment, this is mostly accu- 

 mulated in the fruit and seed, in a concentrated form, for the 

 future consumption, not of the parent plant, but of the new indi- 

 vidual enclosed in the seed. The real and immediate consump- 

 tion of nourishment by the flower, is shown by the action of 

 flowers on the air, so different from that of leaves. While the 

 foliage withdraws carbonic acid from the air, and restores 

 oxygen, flowers take a small portion of oxygen from the air, 

 and give back carbonic acid. While leaves, therefore, purify 

 the air we breathe, flowers contaminate it ; though of course 

 only to a degree which is relatively and absolutely insignificant. 

 When carbon is consumed as fuel, and by the aid of the 

 oxygen of the air converted into carbonic acid, an amount of 

 heat is evolved uniformly and directly proportionate to the 

 quantity of carbon consumed, or of carbonic acid produced. 

 The same amount is more slowly generated in the slower 

 decomposition of an equivalent amount of vegetable matter, 

 by decay, — a heat which is employed by the gardener, when 

 he makes hot-beds of decaying tan or leaves, or by the breathing 

 of animals, where it maintains their elevated temperature. 

 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 propor- 

 tion to the consumption of the oxygen of the air ; or in other 

 words, of the carbon of the plant. The increase of tempera- 

 ture in these cases was measured by common instruments. But 

 now that thermo-electric apparatus affords the means of mea- 

 suring variations inappreciable by the most delicate thermome- 

 ter, the heat generated by any ordinary cluster of blossoms 

 may be detected. The phenomenon is most striking in the 



