392 THE UNIVERSE. 



CHAPTER IY. 



TRANSPIRATION IN PLANTS. 



VEGETABLE physiology approaches very nearly that of 

 animals. Like them, plants exhale moisture abundantly by 

 their whole surface. It is this which, condensed upon the 

 leaves by the cold of night, forms on them limpid little 

 drops of water, which the vulgar incorrectly ascribe to a 

 deposit of atmospheric moisture. 



The idea that plants transpire like animals is due to 

 Muschenbroeck, one of the professors who have contributed 

 most to rendering the University of Leyden illustrious. For 

 this purpose he covered with a plate of lead the whole cir- 

 cumference of the root of a white poppy, so as to prevent 

 the vapor of the earth from interfering with his experiment. 

 The plant was then covered with a bell-glass cemented to 

 the lead. After that, each morning, when the naturalist 

 came to visit the imprisoned plant, he observed that even 

 during the driest nights its leaves were covered with an in- 

 numerable quantity of those drops of water to which the 

 name of dew is given, and that the sides of the glass them- 

 selves were quite obscured with it. It is not, then, from the 

 air that the dew upon the meadow and that upon the leaf 

 comes, but, as the Dutch naturalist discovered, from the 

 transipration of the plants ; dew is nothing else but their 

 perspiration condensed. 



This fact being thoroughly established, it only remained 

 to decide the amount which vegetable transpiration pro- 



