SOME OF THE POSSIBILITIES OF ECONOMIC BOTANY. 643 
make for themselves a home in another.* All but two of the prominent 
weeds of the Eastern States are foreign intruders. 
There are all grades of persistence in these immigrants. Near the 
ballast grounds of every harbor, or the fields close by woolen and paper 
mills where foreign stock is used, you will observe many foreign plants 
which have been introduced by seed. For many of these you will 
search in vain a second year. A few others persist for a year or two 
longer, but with uncertain tenure of the land which they have invaded; 
others still have come to stay. But happily some of the intruders which 
seem at first to gain a firm foothold, lose their ground after a while. 
We have a conspicuous example of this in a hawk-weed, which was very 
threatening in New England two years ago, but is now relaxing its hold. 
Another illustration is afforded by a water plant which we have 
given to the Old World. This plant, called in our botanies Anacharis, 
or Elodea, is so far as | am aware not troublesome in our ponds and 
water ways, but when it was carried to England, perhaps as a plant 
for the aquarium, it was thrown into streams and rivers with a free 
hand. It spread with remarkable rapidity and became such an unmit- 
igated nuisance that it was called a curse. Efforts to extirpate it 
merely increased its rate of growth. Its days of mischief are how- 
ever nearly over, or seem to be drawing to a close, at least so Mr. 
Lynch, of the Botanic Garden in Cambridge, England, and others of 
my informants think. The history of the plant shows that even under 
conditions which so far as we can see, are identical with those under 
which the plant grew in its home, it may for a time take a fresh lease 
of life and thrive with an undreamed-of energy. 
What did Anacharis tind in the waters of England and the continent 
that it did not have at home, and why should its energy begin to wane 
now? 
In Australasia one of the most striking of these intruders is sweet- 
briar. Introduced as a hedge plant it has run over certain lands like 
a weed, and disputes every acre of some arable plats. From the fa- 
cility with which it is propagated, it is almost ineradicable. There is 
something astounding in the manner in which it gains and holds its 
ground. Gorse and brambles and thistles are troublesome in some 
localities, and they prove much less easy to control than in Europe. 
The effect. produced on the mind of the colonist by these intruding 
pests is everywhere the same. Whenever in an examination of the 
plants likely to be worthy of trial in our American dry lands the sub- 
ject was mentioned by me to Australians, I was always ee to be 
* The we an of German gardens and agricultural lands are mostly from Medite rra- 
nean regions, but the invasions in the uncultivated districts are chie ‘fly from America 
(such as Oenothera, Mimulus, Rudbeckia). Handbuch der Pflanzengeographie, von Dr. 
Osear Drude (Stuttgart), 1890, p. 97, 
