7 
This year it has increased so much that the river may be 
said to be full of it; but I must defer a more particular 
account of its behaviour in the Cam and Ouse till next week, 
when, if space permit, I will dispose of the remaining ques- 
tions of whence it came, how it got here, and by what: means 
it is to be got rid of. 
Yours obediently, : 
Ely, August 18, 1852. W. MARSHALL. 
No. III. 
Sir, 
Having in my last, traced this plant from its first discovery 
in Berwickshire in 1842, down to its recent appearance in 
the Cam and Ouse, I propose to devote this letter to a par- 
ticular account of its behaviour in our own rivers, believing 
the chief interest connected with it, to lie in this direction. 
I have already described the Weed as growing in dense 
submerged masses, distinguishable at once from all others 
by its “leaves growing in threes round a slender stringy 
stem ;” and although this brief description is amply suffi- 
cient to identify the troublesome pest, a short further account 
of its appearance and habits may not be uninteresting. The 
colour of the plant is a deep green; the leaves are about half 
an inch long, by an eighth wide, egg-shaped at the point, 
and beset with minute teeth, which cause them to cling. The 
stems are very brittle, so that whenever the plant is disturbed, 
fragments are broken off. Although, at present, it cannot 
propagate itself by seed, its powers of increase are pro- 
digious, as every fragment is capable of becoming an 
independent plant, producing roots and stems, and extending 
itself indefinitely in every direction. Most of our water 
plants require, in order to their increase, to be rooted in the 
bottom or sides of the river or drain in which they are * 
