154 HEAT. 



of a low temperature. In all the cases I have observed, frost 

 coagulates this fluid, collecting it into amorphous masses." 



230. It has been obssrved, that the most succulent plants 

 suffer most readily and most severely by frost. This is 

 thought to be owing to the conducting power ofthe tissue, satu- 

 rated with sap. Hence plants that remain uninjured in dry 

 soils, are very liable to be destroyed by frosts, if raised in 

 damp and shaded situations. It may be adopted by the culti- 

 vator as a fact, that whatever tends to render tissue moist, 

 will increase its power of conducting heat, and consequently 

 augment the susceptibility of plants to the influence of frost ; 

 and whatever tends to diminish their humidity, will also di- 

 minish their conducting power, and with it their susceptibility. 



231. The disenojafjement of caloric durinor the flowering of 

 plants, is a subject of considerable interest, and might, per- 

 haps, with equal propriety, have been noticed under fertiliza- 

 tion ; but as the phenomenon is as yet of doubtful origin, we 

 thought it proper to notice it here. 



The rise of the thermometer when applied to the spadix of 

 the Arums at the timcof flowering, has long been known. 

 Senebier found the temperature 7° higher than the surround- 

 ing atmosphere. Hubert in experiments on the Axum cordi- 

 folium, in the Isle of France, found the thermometer rise from 

 66^, the temperature of the surroundinr atmosphere, to 111*^ 

 when placed in the center of the spa:!ix, and in others to 121°, 

 thus indicating a difference in one case of 45°, and in others 

 of 5d^. The greatest difference was observed to be in the 

 morning. The accurate experiments of Brongniart have 

 rendered it more than probable, that in all cases of flowering, 

 heat is liberated, although from the structure, or size of the 

 flower, it may be impossible to detect it by instruments. It 

 is well known that during the flowering of plant*, oxygen is 

 absorbed, and in some cases this absorption has amounted to 

 thirty times the volume ofthe subject of experiment in twenty- 

 four hours ; during this time carbonic acid is given off. 

 These phenomena plainly indicate the cause of the heat dur- 

 ing the period of fertilization. An enquiry of interest sug- 

 gests itself from these facts, as to the changes effected on the 

 flower by these operations. The disk and petals are now 

 supposed to act an important part in the process of fertiliza- 

 tion, and that the process of fertilization is the same as that 

 of germination. The following conclusion confirms this hy- 

 pothesis. In both cases oxygen is absorbed, and an equal 

 quantity of carbonic acid given off. In both cases amylaceous 



