HEAT. 143 



exhibited in the potato. This tuber when frozen is decidedly 

 sweet, and the starch, which it before possessed in great quan- 

 tities, has, in a great measure, disappeared. 



" Finally, 1 ' says Prof. L., "it appears that frost exercises a 

 specific action upon the latex, destroying the power of motion. 

 If, as Prof. Shultz supposes, this is the vital fluid of plants, such 

 a fact alone would account for the fatal effects of a low tem- 

 perature. In all the cases I have observed, frost coagulates this 

 fluid, collecting it into amorphous masses." 



273. It has been observed, that the most succulent plants 

 sutler most readily and most severely by frost. This is thought 

 to be owing to the conducting power of the tissue, saturated 

 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 cultivator 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 di- 

 minish their humidity will also diminish their conducting power, 

 and with it their susceptibility. 



274. The disengagement of caloric during the flowering of 

 plants is a subject of considerable interest, and might, perhaps, 

 with equal propriety, have been noticed under fertilization ; 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 time of flowering, has long been known. 

 Senebier found the temperature 7° higher than the surrounding 

 atmosphere. Hubert, in experiments on the Arum cordifolium, 

 in the Isle of France, found the thermometer rise from 66°, the 

 temperature of the surrounding atmosphere, to 111° when placed 

 in the center of the spadix, and in others to 121°, thus indica- 

 ting a difference in one case of 45°, and in others of 55°. The 

 greatest difference was observed to be in the morning. The ac- 

 curate 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. 



275. It is well known that during the flowering of plants 

 oxygen is absorbed, and in some cases this absorption has 

 amounted to thirty times the volume of the subject of experi- 



278. What kind of plants suffer most by frost ?— 274. What takes place 

 in the flowering of plants ? Give the experiments with the Arum. — 275. 

 What well-known phenomena during flowering ? 



