THE FLORAL ENVELOPES. 137 



other parts of the flower ; these exercise on the atmosphere, 

 a diflferent kind of influence. Before the appearance of 

 the flowers, the plant is wholly an apparatus of reduction, 

 all its parts being concerned in the assimilation of the food. 

 It decomposes the carbonic acid borrowed from the atmo- 

 sphere and the soil, fixing the carbon and exhaling the oxygen, 

 and forming within its green leaves, young shoots, and super- 

 ficial parts, the substance called chlorophyl. But when the 

 flowers develope, this part of the plant becomes an apparatus 

 of combustion. The starch granules which in the leaves were 

 changed jnto chlorophyl, in the petals are changed into 

 chromule, and become wholly oxidized and converted into 

 saccharine matter. The carbon or sugar accumulated by the 

 nutritive organs of the plant, is consumed by its reproductive 

 organs. Hence we see these matters disappear at the epoch 

 when the flowers expand, and it is therefore necessary to reap 

 those vegetables, which we cultivate for the sugar which they 

 contain, before that period. This disappearance of the saccha- 

 rine store is the result of its slow combustion, or the conver- 

 sion of the carbon of the sugar into carbonic acid. Oxygen is 

 therefore necessarily consumed and heat evolved by the flowers, 

 whilst at the same time carbonic acid rises from them into the 

 atmosphere. Whilst, therefore, the green leaves of plants 

 purify the air, their beautiful flowers contaminate it, although 

 to a degree of course which is relatively insignificant. 



The development of heat by flowers was first observed by 

 Lamarck in the Arum maculatum of Europe. It was afterwards 

 detected by Saussure, in the Bignonia, Gourd, and Tuberose. 

 In these cases the heat was measured by a common ther- 

 mometer. But since the invention of thermo-electric instru- 



