24 Fresh Water Aquarium 



which they inhale and absorb oxygen and 

 exhale carbonic acid, a gas as essential to 

 plant life as oxygen is to animal life. At 

 times the exhalation of oxygen by some of 

 the plants becomes visible. Under the in- 

 fluence of sunlight they become covered 

 with myriads of small silvery beads consist- 

 ing of the purest oxygen. A slight moving 

 of the plants will detach these beads and 

 cause their ascent to the surface of the 

 water. Thus it will be seen that an inter- 

 dependence exists between animal and veg- 

 etable life, the plants absorbing carbonic 

 acid and exhaling oxygen, the animals ab- 

 sorbing oxygen and exhaling carbonic acid. 

 It is therefore indispensable for the welfare 

 of the animals of an aquarium, that it be 

 stocked with plants in the right proportion. 

 Often the amateur may suffer the loss of 

 his most valuable fishes simply because veg- 

 etation in the aquarium is absent or insuffi- 

 cient, in which case either additional veg-eta- 

 tion or an artificial aeration of the water 



