HEAT OF SEEDS AND FLOWERS. 263 



produced by a single seed is too soon carried off by surrounding 

 bodies, to be perceptible, it accumulates to a high degree, when 

 a number are brought together, as in the process of malting 

 (. 283,4), in which the thermometer has been seen to rise to 

 110. The same may be said of that other period of vegetation, 

 in which an extraordinary amount of carbonic acid is evolved, 

 that of flowering (. 285). It is evident that, from the little 

 substance of the parts thus heated, and the large amount of sur- 

 face they expose to the air, the heat will be carried off by the 

 atmosphere, almost as rapidly as it is produced. Still in some 

 flowers, a considerable amount of heat can be proved by the 

 thermometer to be disengaged ; thus, a Geranium has been found 

 to possess a heat of 87, when the air around was at 81. 



412. As in the case of seeds, however, the production of 

 heat is most sensible, when a number of flowers are crowded 

 together ; and this is still more the case, when they are inclosed 

 in any general covering, as are those of the Arum family. In 

 these the flowers are small, and are very closely set upon a 

 stalk, which is called a spadix ; and the whole cluster is sur- 

 rounded by a large leafy sheath called a spathe. It is in these 

 flowers, that the size of the fleshy disk is the most considerable, 

 and the quantity of carbon to be united with oxygen is therefore 

 the greatest ; and the combination of this cause with the other 

 occasions the temperature of the clusters to be raised very high. 

 A thermometer placed in the centre of five spadixes has been 

 seen to rise to 111, and one in the centre of twelve to 121, 

 while the temperature of the external air was only 66. The 

 increase of temperature commences with the opening of the 

 flower ; and it is greatest at the time of the shedding of the 

 pollen (. 433). 



413. That the development of heat in these cases is owing 

 to the conversion of carbon into carbonic acid, is proved by two 

 kinds of experiments. In one, the cluster of flowers was placed 

 in pure oxygen, by which this change was performed much more 

 rapidly than in common air ; and the heat given out was much 

 greater, than that evolved by a flower-stem at the same stage, 

 in common air. On the other hand, a spadix being put into 



