352 Foreign Trees and Plants [July? 



stiffest part of the London clay. Probably every piece of cultivated 

 ground, which contains a laburnum tree, produces each spring a 

 plentiful crop of self-sown young trees, which come up without 

 the least care or protection until destroyed in the process of weed- 

 ing ; yet the laburnum shows no disposition to take a place among 

 the naturalised trees of our woods and hedges, although the seeds 

 must often be carried there by birds. It is remarkable that many 

 of our common vegetables, the cabbage, the asparagus, the sea-kale, 

 the celery, are natives of our own shores, never growing sponta- 

 neously out of reach of the salt spray ; and yet requiring, when 

 transplanted into our gardens, no peculiarity of soil or treatment 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 propagate themselves with us or spread, 

 except under man's protection. 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 expulsion 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 as 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 naturalisation has occurred 

 in the case of the Elodea canadensis 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 

 navigation. Other instances might be mentioned of foreign plants 

 introduced with seed having in a very short time become common 

 weeds in all cultivated 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 naturalised aliens. 



There is no doubt we have a great deal to learn as to the mode 

 in which plants propagate themselves in nature, which may be of 

 the utmost value to our gardeners. Every one is familiar with the 

 fact of the apparently spontaneous appearance, in immense abun- 

 dance, of plants in soil when subjected to certain farming operations, 

 or on the sowing of some particular crop. Whenever a new rail- 

 way cutting or embankment is made, some plant unknown in the 

 neighbourhood is almost sure to appear, and either permanently 



