THE AQUARIUM AND WATER PLANTS. 281 



all pretty plants, of easy cultivation. Those most com- 

 monly met with are perfoliatus, fluitans, natans, and 

 heterophyllus. They bloom above water, and need 

 constant thinning, or they would occupy the whole 

 tank. 



Potamogeton. 



The pretty Sagittaria, or Arrowhead, producing its spike 

 of white flowers in August, should not be overlooked, 

 or its near neighbor on the river shallows, the Pickerel 

 Weed (Pontederia Cordatd}, so conspicuous for its purple 

 flowers from July until autumn. 

 24* 



