ACCLIMATIZATION OF FOREIGN TREES AND PLANTS. 531 
birds. It is remarkable that many of our common vegeta- 
bles, the cabbage, the asparagus, the sea-kale, the celery, 
are natives of our own shores, never growing spontaneously 
out of reach of the salt spray; and yet requiring, when 
transplanted into our gardens, no peculiarity of soil or treat- 
ment to enable them to support a vigorous existence. These. 
are instances of plants to which our climate appears entirely 
congenial, and yet which seem as if they could not propa- 
gate themselves with us or spread, except under man's pro- 
tection. Others, again, appear to require only to get a 
footing in a foreign soil to become established in it with 
extraordinary rapidity, even to the overmastering or expul- 
sion of some of the indigenous inhabitants. When Australia 
and New Zealand were first colonized by Europeans, their 
flora presented an aspect of perfect strangeness, very few of 
the native trees or flowers belonging even to genera common 
to Europe. The seeds of some of our English weeds were, 
however, introduced, intentionally or accidentally, by the 
early settlers; and now the thistle covers the waste lands of 
Australia as it does in England, and the clover and the 
groundsel everywhere remind the Englishman of his far- 
away home, and have become às completely at home as the 
mustangs or wild-horses on the pampas of South America. 
In our own country a very remarkable instance of this rapid 
naturalization has occurred in the case of the Elodea Cana- 
densis or Canadian water-weed ; which, introduced not many 
years since into our canals from Canada, has now become 
such a pest in many places as seriously to impede the navi- 
gation. Other instances might be mentioned of foreign 
plants introduced with seed having in a very short time be- 
come common weeds in all eultivated land. Indeed, many 
of the species included in our handbooks of British plants 
are so entirely confined to arable land or to spots in the 
immediate vicinity of human dwellings, that it is impossible 
to say how many of them may be really indigenous to the 
soil, and how many naturalized aliens. 
