709 



or drain in vvliicli they are found ; but this is independent altogether 

 of that condition, and actually grows as it travels slowly down the 

 stream, after being cut. The specific gravdty of it is so nearly that of 

 water, that it is more disposed to sink than float ; and the cut masses 

 may be seen under water, either on or near the bottom, rolling over 

 and over like wool-packs, clinging to everything they meet with, and 

 accumulating in great quantities at locks and bridges (hugging the 

 piers of the latter), and grounding in shoal-water. Its mode of growth 

 may be best seen in still and narrow waters (such as the stream above 

 the mills at Cambridge), where it seems to spring, first from the two 

 sides and bottom, meeting at length in the middle, and completely 

 filling up the watercourse, as I have seen in some cases, almost to the 

 exclusion of the water. Except in very quiet places, it is not likely 

 to be found in flowei'. I have, however, found it flowering in great 

 profusion just below Ely ; but, as the plant is dioecious {i. e., pro- 

 ducing male and female flowers on separate individuals), there is no 

 fear, as I have before remarked, of its producing seeds in this country, 

 all the specimens hitherto found being of one sex only. 



Although there is little doubt that in 1850, and perhaps in 1849, it 

 might have been detected in our rivers, if diligently sought for, it does 

 not appear to have attracted the notice of watermen and the staff" of 

 fen officials, whose duty it is to cut the weeds in the summer time, 

 till last year, when it was noticed, in considerable quantities, all the 

 way from Small Bridges down to Bottisham Lock, but not to one-third 

 its present extent. I have been infonned, however, that even last year 

 it was raked out of the river near Waterbeach and Ditton, and carted 

 away for manure. At the present time it needs no longer to be sought 

 for; it may be found everywhere, in more or less quantity, from Cam- 

 bridge downwards, choking up the mouths of docks, sluices, and nar- 

 row watercourses, and in the upper portions of the river impeding both 

 navigation and drainage. Perhaps its wonderful and rapid increase 

 this year may be owing to the excess of wet, and the long continuance 

 of hot weather raising the temperature of the water to an unusual de- 

 gree ; but, if it should continue to increase in anything like the same 

 ratio as it as done, the upper parts of our rivers will no longer be able 

 to pass their waters to sea, and the navigation interest may surrender 

 to the railways what little remains to them of the carrying trade. 



That it is already a source of annoyance to our watermen, is evident 

 by the universal complaints which have been made of the obstructed 

 state of the River Cam. I am told that the river at the backs of the 



