206 HYDROCHARIDACEtE 



of recent introduction into this kingdom, is now generally distributed. It is 

 an aquatic, forming thick, entangled, submerged masses of considerable 

 extent, and so heavy, that when cut, instead of rising, like most water- 

 plants, to the surface, or floating onwards to the sea, it falls immediately to 

 the bottom. Its slender whorled leaves are of a rather light green, and as 

 thin as some of our grass-green seaweeds, growing on a long, brittle, round, 

 almost transparent stem, which branches in all directions, sending out at 

 intervals its fibrous roots, and bearing among its whorls of leaves, from May 

 to September, very small pinkish-green flowers. The whole plant, both in 

 form and structure, is readily distinguished from every other of our native 

 aquatics. 



The smallest portion of this plant, having the root attached, will, if 

 broken off, propagate itself immediately ; and the history of the progress of 

 this weed is now well known, and has become a matter of painful interest to 

 many in this kingdom, though the mode of its introduction still remains a 

 mystery. It is identical with the American aquatic termed Udora canadensis 

 by Nuttall, and Elodea canadensis by other authors, and was originally dis- 

 covered in this country by the late Dr. George Johnston of Berwick, in 1842, 

 in the lake of Duiise Castle, Berwickshire, though it had been found in 

 County Down six years earlier. The attention of several scientific men was 

 called to the plant, but for several years nothing further was heard of it, 

 till it was seen again by Miss Kirby, in 1847, in the reservoirs adjoining the 

 Foxton locks on the canal near Market Harborough, in Leicestershire ; and 

 as the locks had been cleansed about two years before, there was reason to 

 believe that its introduction had been recent, although at that time it had 

 become abundant in the water. Mr. Babington then published an account 

 of this plant, and Dr. Johnston, on reading it, immediately recognised the 

 description to be that of the same weed which he had seen some years 

 before. On examining the loch of Dunse Castle, he found that this water- 

 weed had not only accumulated there in great profusion, but that, having 

 made its way out of the loch, it was forming matted patches in several 

 places down the Whiteadder, in its course to the Tweed. In the same 

 season it had appeared in the Nene, a tributary to the Trent in Nottingham- 

 shire ; and propagating itself with its usual rapidity, it soon formed so large 

 an amount of aquatic herbage, that it threatened to block up one of the two 

 streams into which the Trent there divides; while in the Trent itself it 

 afterwards grew in such profusion, that in some parts of the river fishing 

 became quite impracticable, the fishermen finding their gear unable to com- 

 pete with this new and formidable vegetable hindrance. This plant was also 

 found in the Watford locks, in Northamptonshire, growing in numerous and 

 immense tangled masses. 



It was in the summer of 1849 that this troublesome water- weed was first 

 discovered in Derbyshire and Staffordshire, where it formed, as it were, small 

 e;reen meadows on the water, both in the Trent and the adjoining canals ; in 

 1850 it had gathered in profusion near Rugby in Warwickshire, and in the 

 following year it had appeared in the Cam at Cambridge, behind the colleges, 

 and by its growth so clogged up the river, that the barges which had to 

 make their way through its clumps required the aid of extra horses. The 



