LKCT. It.] VITAL FUNCTIONS OP PLANTS. 63 



plant ; for, if the newly evolved leaves of a tree be 

 attacked by severe frost, they also mortify, and 

 drop from the sound twig. Vegetables resist heat 

 also ; for, a vine which is nailed on a wall will feel 

 cool, when the wall can scarcely be touched on 

 account of its heat : and fruits hanging in the sun 

 remain cool, when a glass full of water placed in 

 the same situation is quickly heated*. Mr. John 

 Hunter found, by experiment, that while the 

 thermometer stood under 56 in the open air, the 

 temperature of plants, tried by placing the bulb 

 of the instrument within them, was always above 

 that degree, but under it when the weather was 

 warm. Plants are, however, very susceptible of 

 the impressions of heat ; and feel its effects, as an 

 agent acting on their vital energy, even partially ; 

 so that one part of a plant may be leafless, and in 

 a state of inaction or torpidity, whilst another part 

 is clothed with foliage. If some of the branches 

 of a vine, for example, which is growing on the 

 outside of a hothouse, be taken into the house, 

 these will be covered with leaves very early in 

 spring, whilst those that are exposed to the 

 weather remain naked, and in the same state as 

 other plants, growing in the open air, in that season. 



* Mr. Forster, who sailed with Captain Cook, found the 

 ground near a volcano, in the island of Tanna, so hot as to raise 

 Fahrenheit's thermometer to 210 ; and, at the same time, 

 this spot was covered with flowers. 



