TROPICAL AQUARIUM FISHES 17 
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Fic. 127. PotTAMOGETON DENSUs (Reduced one-half) 
Fic. 128. Nrirerta cRAcILIs (Reduced one-third) 
POTAMOGETON 
In strong contrast to the foregoing dainty plants is Potamogeton 
densus, or pondweed. As will be seen from figure 127, these leaves are 
broad and robust. In color they are a bright green. This variety is said 
to be of European origin but is now common in ponds in the United 
States. If established in soil in flat pots it. flourishes in a well-lighted 
aquarium. Pieces collected from the wild may be introduced by fasten- 
ing into the sand. They present a very attractive appearance and will last 
for quite a time, but should only be regarded as temporary and when the 
leaves begin to turn yellow should be removed. There are many widely 
distributed species of Potamogeton, all looking very attractive in a state 
of Nature, especially P. crispus with curly leaves. They look very tempt- 
ing, but none seem to survive in the aquarium except P. densus and that 
only when established just to its liking. 
