AMERICAN IMMIGRANTS.
MORE or less fanciful analogies have frequently been traced between the keen commercial competition among nations and the struggle for existence in the world of Nature. It is a significant circumstance that, at any rate so far as plants are concerned, the soil of Britain furnishes an even more congenial foothold for American than for European immigrants whenever they have been introduced, whether by human agency or otherwise. For instance, the well-known Canadian waterweed was introduced in 1836, and immediately flourished and multiplied to such an extent as to threaten to choke all our waterways, and perhaps conduced as much as the competition of the railways to check the natural development of our canal system. However, after its first riotous luxuriance in its new surroundings an inclination to a decline in vigour seems to have set probably due to the fact that its reproduction in Europe proceeds by budding or division and not by the formation of seeds, for at present only the female plant has to come to our shores. Similarly the Virginian creeper, whose name betrays its American origin, is unable to ripen its grapes ; yet it thrives even in London with all the unrestrainettluxuriance of a weed, festooning and beauti- fying the meanest backyard of a London slum, and spreading by means of stem-roots, which develop whenever the creeping stems come in contact with the earth. Yet another American colonist, a pretty orange balsam, may be seen not far from London along the banks of the Wey and other Surrey streams. Unlike the plants already mentioned, it is able to set abundant seeds, thoroughly capable of germination. The American wood-sorrel with yellow flowers has become permanently established in England ; and another small weed, the trailing claytonia, with a white flower, has come from the States and spread far and wide in this country. The Canadian Michaelmas daisy has also come to stay in our Southern counties. Some of our naturalised American plants have doubtless been introduced unwittingly; others, such as the evening primrose and the yellow mimulus or monkey plant, are clearly garden-escapes and are a great addition to our flora. The visitor to Leith Hill in September may remember a pine-wood at Friday Street where be will suddenly come upon a silent pool covered with the golden bloom of the mimulus floating on its waters. Certain American plants have managed to travel as far as Ireland, but occur nowhere else in Europe. All of them are plants fond of damp situa- tions, and comprise a pond-weed, a small white orchid allied to our lady's tresses, and little blue grass-lilies from Bermuda and California. These must doubtless have arrived independently of human agency, probably owing to seeds adhering to the feet of aquatic American birds who have performed the journey willingly or unwillingly. Linnaeus, indeed, once recorded that the seeds of the West Indian filbert germinated after haying been stranded by the Gulf Stream on the Norwegian coast; and two American water-plants have become thoroughly naturalised in the lakelets of the Hebrides and the West of Ireland, but nowhere else in Britain. This occurrence, and the fact, however, that there are three American fresh- water sponges which have also established themselves in the West of Ireland, render it much more likely that the birds, and not the ocean currents, have been the agents of com- munication.
A far greater problem is the presence in the Mitchelstown caves in Tipperary of a spider and some small insects which are indistinguishable from species occurring in the Kentucky and other American caves. Here it would be out of the question to assume a migration of creatures which live exclusively in so gloomy a habitat. Perhaps they are the deseendantc of species which took to troglodyte habits in the far-distant epoch before the glacial period, when North America was connected with the British Islands through Iceland and the Faroes. The great uniformity of surround- ings of cave-life would very likely check any tendency to variation, and might, so to speak, stereotype the species. Insects are by the nature of things less ready than plants to feel at home on a foreign soil, usually owing to the absence of suitable food-plants ; yet certain American long. horned beetles have been recorded in Ireland, flourishing in ash-trees. The importation of timber is, however, the most common means of introducing insects. A North American butterfly, the large and handsome Anosia menippe, with marked migratory habits, has been captured many times in England, and, indeed, is now regarded as almost naturalised here. It is an insect of powerful flight, and would probably secure a firmer footing if only the numbers of collectors were in inverse ratio to the abundance of the food-plant of its cater- pillar. Many will remember the scare among agriculturists in the " seventies " on the appearance of the destructive Colorado beetle in some potato-fields ; fortunately, the invasion was unsuccessful and easily repressed. Its fellow. citizen, the Hessian fly, has, however, managed to found a settlement in the wheatfields of this country, but the devasta- tion has not as yet been severe or widespread. It is truly American, but it received its name from the unfounded belief that it was introduced about 1776 with the baggage brought by the Hessian troops employed by the English Govern- ment.
On the Continent, however, more American plants have become naturalised than in England,—for instance, the Canadian species of golden rod and Michaelmas daisy, and other garden-escapes; and the Mexican agave, often called an aloe, has become thoroughly established in the Mediter- ranean region. Perhaps if Britain enjoyed a drier climate or were less thickly populated, American species would have a still better chance of demonstrating their vigour and adapt. ability to a foreign soil, and in course of time might exercise an appreciable influence on the character of our flora and fauna. Yet we have, at any rate, the consolation that none of the new immigrants into Britain have shown a similar luxuriance of growth to that of British species in the Antipodes. The appalling numbers of the prolific rabbit in Australia, and the equally amazing development of the thistle in New Zealand, are facts known to everybody; nettle, plantain, and chickweed follow everywhere in the footsteps of the white man, taking the place of native weeds, and, as an offset to the spread of the Canadian waterweed in England, our humble watercress has developed in New Zealand rivers to the astonishing length of twelve feet or more, with stems an inch in thickness. The superior vitality of the European over the neighbouring Australian flora is still further shown by the fact that whilst nearly two hundred European plants have made themselves at home in New Zealand, not more than two or three Australian species have been able to establish themselves there, in spite of many attempts made to naturalise common Australian plants and trees.
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