ON ANACHARIS ALSINASTRUM. 363 
canals that the entire canal is grown up with it in masses suffi- 
cient to obstruct anything in the shape of a boat ; and even there, 
from its fragility, it is very little real obstruction, and readily 
gives way to anything touching it, not clinging to the sides of a 
boat or swimmer as some of the Potamogetons do: the obstruc- 
tion caused by P. perfoliatus, P. crispus, P.. lucens, and P. fla- 
beilatus, to the passage of a small boat, I have proved to be much 
ereater than the thickest mat of Anacharis I could find. How 
it can obstruct the drainage of the Fens I cannot see, as it will 
uot lie close enough together for even capillary attraction to act 
and so keep as great a bulk of water as itself together. If a 
quantity be raised from the water on a stick, it is found that the 
water quickly runs from it; 1t would require a very large quan- 
tity to make a dam solid enough to keep water a foot higher 
than its usual level. In September, 1853, a very large plantation 
of Anacharis, about twenty-six square yards in extent, was taken 
possession of by a few ducks which refused to feed on any other 
part of the canal; they were probably in search of the insects 
which had taken shelter amongst the entangled mass (I have 
generally found the beautiful Bell Polype on the edge of its 
leaves). Be that as it may, it was not able to withstand the 
assault from their bills, and gradually disappeared, so that by 
October there was not a morsel in the part of the canal they fre- 
quented. It commenced growing again about October, 1854, and 
in the spring of 1855 was again cleared by the ducks. The only 
places it is likely to be a serious nuisance are ponds and orna- 
mental water generally ; but it is easy to eradicate the plant in 
these places, which are most of them provided with a sluice for 
drawing off the water. The Avon being a mill-stream, the mills, 
as a matter of course, sometimes want repairs. Bridges and locks 
too wear out, so that we sometimes have the water drawn off as 
low as possible, when a great portion of the Anacharis is left dry 
for a time, varying from twelve to twenty-four hours. In 1855 
repairs of the foot-bridge caused the river to be kept low a longer 
time than usual, when a very wide and shallow portion of the 
river which was overgrown with Anacharis became entirely free 
from it. When the plant has flowered it soon decays. In the 
eanal, where it flowered in 1853, soon after the flowers were over 
it became very weak, the leaves falling off, and the winter flushes 
carried most of the denuded stems away. This I have seen repeat- 
