MANAGEMENT OF AQUAEIUMS 247 



plants are necessary as an equipment for an 

 aquarium, as they are both beautifiers and 

 oxygen producers, "Without their help it would 

 not always be safe to allow the water to re- 

 main in an aquarium for an indefinite period 

 without changing it. 



Of the plants which grow in sand or gravel 

 three stand forth prominently as the most 

 valuable. They are the anacharis or water- 

 weed, the sagittarias, and the ludwigias. 

 These three all give forth a great amount of 

 oxygen, and are beautiful and of rapid growth. 

 The anacharis in particular is such a vigorous 

 grower that often in a few weeks, when the 

 sunshine is bright and the water warm, it will 

 have to be thinned out. The Anacharis can- 

 adensis is the best species, and has dark green, 

 ovate leaves, with light stems. 



The sagittaria resembles somewhat the well 

 known vallisneria, or giant eel-grass, but it is 

 considered as a better oxygenator and does not 

 fill up an aquarium as rapidly as the eel-grass. 

 'Sagittaria napana is as indispensable for 

 oxygenating purposes as the anacharis, to 

 which it also forms a very strong contrast in 



