30 THE AQUAVIVARIUM. 



has a curious history. Up to the year 1842, it 

 had never been noticed in Great Britain ; now it 

 is a common weed in our ponds, ditches, and 

 rivers. The first recorded instance of its being 

 found, was by the late Dr. George Johnston, of 

 Berwick-upon-Tweed, in a pond at Dunse Castle, 

 Berwickshire, in July, 1842. In 1848, he again 

 found the same plant in the river Whiteadder, 

 about five miles from the last locality. In the 

 same year it was discovered in the river Lea 1 , 

 near Nottingham, and since then has been found 

 in various new localities. Dr. Johnston sent 

 some of his specimens to Mr. Babington, at 

 Cambridge, which, thriving in the Botanic 

 Gardens, they were turned out into the Cam, 

 and the plant has become most abundant in that 

 river. From Kew Gardens it has escaped into 

 the Thames, and it may be now regarded as one 

 of our most common and troublesome water- 

 weeds. This plant grows abundantly in North 

 America, where it was described by Nuttall 

 under the name of Udora canadensis. The 

 genus had, however, been previously described 

 by Richard under the name of Anacharis. Only 

 the pistilliferous plants have been seen in this 

 country. From this and other circumstances, it 

 has been concluded that this plant must have 

 been introduced into this country probably with 

 timber from America. Be this as it may, it is 

 very useful for our Aquavivarium. It grows 

 vigorously, looks very pretty, and is a capital 

 aerator of the water. Its great fault is, that it 

 grows so very vigorously, that it chokes other 

 plants. It needs, therefore, keeping down. It 

 roots in the soil, but will grow whilst floating. 

 It has drooping stems, which are covered with 

 small oblong-oval leaves, three or four in a 



