WATEE-PLANTS. 



67 



checking its undue growth in streams and ponds. In an 



aquarium it should not be allowed to float, for it will make the 



water look untidy; small pieces ought to be planted at the 



bottom. If the tank has been filled with water before the 



introduction of this plant, a small 



stone may be tied to the end of a 



short spray and sunk where it is 



iatended to grow, and it wUl quickly 



take root; but it must be watched, lest 



it occupy, through its rapid increase, 



more than its share in the tank. 



In concluding my remarks on the 

 Anacharis, I will venture to remind 

 the aquarium-keeper that he should 

 be exceedingly careful not to be the 

 cause of the introduction of this 

 plant into the streams and ponds 

 of his neighbourhood. All that he 

 does not require ought to be com- 

 pletely destroyed, and not thrown 

 carelessly away; for the smallest 

 portion of this most vigorous weed, 

 being conveyed either by accident or 

 otherwise to any permanent piece 

 of water, may quickly become quite 

 a nuisance there. 



The Mare's-tail (Hippuris vul- 

 garis) (Fig. 48) is only useful and 

 ornamental in an aquarium imtil 

 after it has flowered, when it sinks 

 to the bottom, and should be re- 

 moved. It ought to be planted in 

 a pot containing loam mixed with 



silver sand and covered with a layer of gravel; the weed 

 can then be easily taken away, when its duty has been done, 

 without disarranging the aquarium. As this plant rises 

 several inches above the surface of the water, it should not 

 be introduced into a tank which has a covering. The 



p 2 



Fig. 48. Mare's-tail 

 (Hippuris vulgaris). 



