140 
THE AMEBIC AN WATER- WEED. 
[Nature and Art, May 1, 1867. 
pendent Press,” * thus speaks of it : — “ A re- 
markable plant has recently made its appearance in 
the rivers Ouse and Cam, and already abounds to 
such a degree, as not only to impede navigation, but, 
what is of far more importance in this fen country, 
to threaten injury to our drainage.” In Letter III. 
he speaks of it “ growing in dense submerged 
masses, distinguishable at once from all other 
weeds by its leaves growing in threes round a 
slender stringy stem. 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 when- 
ever the plant is disturbed fragments are broken 
off. Although at present it cannot propagate 
itself by seed, its powers of increase are prodigious, 
as every fragment is capable of becoming an in- 
dependent plant, producing roots and stems, and 
extending itself indefinitely on every direction.” 
Mr. Marshall speaks of it as having been a great 
source of annoyance to the watermen of the Cam, 
to sluice- keepers, to rowers, and to swimmers. 
Since that gentleman published his pamphlet 
on this water-weed in 1852, the Anacharis has 
spread far and wide, and has now become common 
in almost every canal, stream, and pond; causing, 
in some cases, a very great amount of incon- 
venience to navigation, besides choking up our fish- 
ponds, &c. &c. 
The rapid spread of the Anacharis is easy 
enough to account for, when we consider how, on 
the one hand, the kingdom is intersected with 
rivers, canals, and streams, which often commu- 
nicate with each other, and how readily the smallest 
bits of the weed grow without any root at all. 
But the question as to its mode of introduction 
into this country is not so easily answered. I ought 
to say that some botanists have affirmed that it is 
no foreigner at all, but a true native ; but this idea 
is improbable. The Anacharis alsinastrum is the 
Elodea Canadensis of North America, where, with 
other species or allied genera, it is common in the 
rivers. From North America, then, it is most 
probable our plant originally came ; but how did it 
get here 1 
There are, as Mr. Marshall says, “ various ways 
in which a plant may be imported. A botanist, 
in the ardour of that botanical instinct which 
prompts him to surround himself with as many as 
possible of the beautiful and varied foi’ms of vege- 
table life, might have introduced it ; but we have 
no evidence that such has been the case, although 
botanists have been known to do such things.” 
The same writer thinks it most probable that the 
Anacharis was introduced at or about Rugby with 
American timber, during the execution of some of 
the numerous railways which meet at that point. 
“ We know,” he adds, “that in North America the 
timber is floated down the rivers, in which case 
fragments of the American weed would cling to it, 
* See Mr. Marshall’s Pamphlet on “ The New Water- 
weed.” London : W. Pamplin, 1852. 
or seeds might find their way into the clefts of the 
wood, and if but one seed or one fragment retained 
its vitality in some moist cranny till it reached its 
final' destination, I verily believe it would be 
sufficient to account for the myriads of individuals 
that now exist in England.” 
But it is useless to speculate ; the real mode of 
its introduction will probably never be known. 
And now we have to account for the presence of 
the male plant in this country. Hitherto all the 
individuals observed have been females; but Mr. 
Bentham and Dr. Oliver tell me that the male 
plant has, they believe, made its appearance some- 
where in the neighbourhood of London during the 
last summer. This is not very pleasant news, for 
the one sex was troublesome enough. The question 
as to how the Anacharis came into the Cam is 
easily answered : — 
“ In 1847 a specimen from the Foxton locks was planted 
in a tub in the Cambridge Botanical Garden, and in 1848 
the late Mr. Murray, the Curator, placed a piece of it in 
the Conduit stream that passes by the new garden. In the 
following year, on Mr. Babington asking what had become 
of the stick which marked the site of the plant, he was 
informed that it had spread all over the ditch. From this 
point it doubtless escaped by the waste-pipe across the 
Trumpington road into the 1 Vicar’s Brook,’ and from thence 
into the river above the mills, where it is now found in the 
greatest profusion. In the case of the Cam, then, we see it 
proved to demonstration that the short space of four years 
has been sufficient for one small piece of the Anacharis to 
multiply so as to impede both navigation and drainage.” 
I first noticed this weed in the Shropshire Union 
Canal about two miles from Newport, about ten 
years ago; it grew in dense patches here and there. 
Since that time, till within a year or two ago, it 
grew to such an extent as to destroy almost all 
other aquatic vegetation. In the “struggle of 
life,” the Potamogfetons, the Myriophyllums, and 
the Water Ranunculuses, disappeared, leaving the 
Anacharis almost the sole occupant of the water. 
It used to flower abundantly from July to the end of 
September, in several places in the canal, but within 
the last two years or so the Anacharis has almost 
disappeared ; and when I wanted specimens in 
blossom last autumn for examination, I had to go 
for them to another branch of the canal, four miles 
distant, as I could find none where formerly they 
were so abundant. The Potamogetons and Myrio- 
pbyllums have since returned. What has been the 
cause of the disappearance of the Anacharis ? That 
the swans eat great quantities of this weed I have 
repeatedly seen; but then there was the same 
number of swans in the canal when the weed was 
so luxuriant. Pond snails — as the Lymnei — eat the 
weed; and whether it has been unable to bear up 
against the repeated attacks of swan and snail, I 
know not : probably to this cause in part, and 
partly to the fact that quantities are taken out by 
the canal-keepers and by nets, we must attribute 
its disappearance. 
The Anacharis is one of those plants in which 
the so-called “circulation” may be conveniently 
observed. This curious movement of the chloro- 
phyll granules, so familiar to microscopic observers 
