THE AMERICAN WATER WEED. 131 
prevent water-fowl swimming across. Thoroughly dredged 
out in autumn of same year. 
1868 Same pond again full; water now drained off, and bottom 
thoroughly cleaned. 
1870 Stream running through Ball’s Knolls Meadows full of it. 
1873 Choked out all other vegetation from ditches in Queen’s Park 
Meadows, and ponds in Saltney Fields. 
' 1884 Still frequent in all the above localities, but far less abundant than 
formerly. 
| 1867 Large fishpond in front of Eaton Hall so choked with it as to 
§ 
LOCAL NOTES. 
The last observation applies equally to all recorded instances 
of its occurrence where its natural progress has not been inter- 
fered with by attempts at its extermination The experience of 
those who have had most to do with it seems to indicate that if 
left alone, its habit is, upon first introduction into a new locality, 
to spread with alarming rapidity; so much so as literally to 
choke other water plants out of existence. But this active phase 
reaches a maximum in from five to seven years, and then 
gradually declines, until at last the Anacharis ceases to be a pest, 
and becomes an ordinary denizen of the pond, river, or canal, as 
the case may be. 
Remembering the unisexual nature of the plant, and the 
peculiarities of its structure, how are we to account for it becom- 
ing so enormously abundant here, while it shows no such 
tendency in its native country? And, further, having once be- 
come so abundant, how are we to account for its subsequent 
diminution? The rapid increase I believe to be due to the 
following causes :— 
a. Our rivers are slower, shallower, and contain more nitro- 
-genous matter than the deeper rapid rivers of America ; 
therefore it finds ample food, and is less often com- 
pletely cleared away by powerful currents. 
6. Our winters are milder, therefore permitting a longer 
period of growth. 
c. Virgin soil (other conditions being favourable), or water, 
has a well known and notable effect in promoting in- 
creased growth. 
d. British specimens of Anacharis do not produce seed, 
which is always an exhaustive process in vegetable 
life. Plants or even animals hindered from sexual 
reproduction commonly exhibit abnormal conditions of 
size and longevity. Annual plants may often be 
made biennial or even perennial by preventing them 
from seeding. 
e. Every fragment has the power of continuing the life of 
the plant. The axillary glands probably performing 
for such fragments the nitrogen absorbing functions 
commonly performed by roots ; enabling the plant to 
live and grow for lengthened periods without any 
roots at all. 
