60 THE AQUARIUM. 



action takes place only under the influence of light, 

 as during the night the contrary occurs, the leaves 

 giving out carbon and absorbing oxygen, although in 

 very small quantities compared with what is emitted 

 during the daytime. 



If a bunch of leaves be introduced into a jar of 

 air which has been deprived of its vitality by means 

 of animal respiration, and the jar exposed to the rays 

 of the sun, the air will, in a few hours, again become 

 pure and wholesome. 



The same principle holds good in aquatic plants, 

 many of them having the power of keeping the water 

 in which they grow from becoming impure or foul. 



In ponds where there is no regular supply of fresh 

 water from running streams, it has been noticed that, 

 during the winter, when the plants are dead, the fish 

 frequently come to the surface to breathe, while in 

 the summer, when the plants are growing, the vitality 

 of the water is preserved. 



It is upon this wonderful law of Nature that the 

 aquarium, that endless source of amusement and in- 

 struction, is based; and although it is as much 

 intended to illustrate the functions of animal as of 

 vegetable life, perhaps the following account, taken 

 from a beautiful work, entitled " Ocean and River 

 Gardens," descriptive of the principles upon which 

 it is conducted, may be interesting to the reader. 



" The successful treatment of aquatic plants and 

 animals, in the confined space of a glass aquarium, 

 depends entirely upon the discovery that there exists 

 in Nature a self-adjusting balance between the supply 



