THE ORNAMENTAL PLANTS — WINDOW-GARDENS 349 



making and keeping an aquarium: (1) The equilibrium between 

 plant and animal life must be secured and maintained; (2) the 

 aquarium must be open on top to the air or well ventilated; 

 (3) the temperature should be kept between 40° and 50° for 

 ordinary animals and plants (do not place in full sun in a hot 

 window) ; (4) it is well to choose such animals for the aquarium 

 as are adapted to life in still water; (5) the water must be kept 

 fresh, either by the proper balance of plant and animal hfe or 

 by changing the water frequently, or by both. 



The aquatic plants of the neighborhood may be kept in the 

 aquarium, — such things as myriophyllums, charas, eel-grass, 

 duckmeats or lemnas, cabomba or fish grass, arrow-leafs or sagit- 

 taria, and the like; also the parrot's feather, to be bought of 

 florists (a species of myriophyllum) . Of animals, there are 

 fishes (particularly minnows), water insects, tadpoles, clams, 

 snails. If the proper balance is maintained between plant and 

 animal life, it will not be necessary to change the water so fre- 

 quently. 



