FRESH-WATER AQUARIUM. 57 



no time in grappling with the common enemy." It lias only 

 been known ten years in England, and yet has already 

 become a common weed, affecting the traffic of rivers and 

 canals, impeding the currents of minor streams, and filling 

 up isolated ponds, thus growing in both running and still 

 water, and though it seems to prefer the former, grows the 

 more rapidly in the latter. It has already rendered the 

 Thames in some parts almost impassable. 



The above supposition of Mr. Marshall's of its introduc- 

 tion into England seems, however, not to be the correct 

 one, as I find the following given in a little book on the 

 Aquarium, published by Messrs. Dean & Son, of London : 

 " One of the Cambridge professors, having received a plant 

 from a friend in Canada, kept it for some time in a glass 

 jar : but not seeing any particular use in retaining it, 

 threw it away down a drain that emptied itself into the 

 Cam. The following year a great stir was made about a 

 new weed, which was fast choking up that river ; and, 

 upon inspection, the professor was much surprised to find 

 in it his old acquaintance, which he had the year before 

 parted with so unceremoniously." 



The Chakace.i: arc all of them excellent plants for use 

 in an Aquarium. Dr. Lankcstcr gives the following general 

 description of the species : " All the species arc easily 

 known in the water by consisting of a central branch, 

 which is composed of elongated cellular tubes, and at the 

 junction of each tube with the other it gives off a series 

 of branches, which surround the primary tube in the form 

 of a whorl. In the axils formed by the branches with the 

 primary stem, the parts which represent the stamens and 



