Page:Popular Science Monthly Volume 40.djvu/229

Rh of useful plants into Australasia have been aided largely by his convenient treatise on economic plants. It may be said in connection with the fodder-plants, especially, that much which the baron has written can be applied mutatis mutandis to parts of our own country.

The important subject of introducing fodder-plants has been purposely reserved to the last because it permits us to examine a practical point of great interest. This is the caution which it is thought necessary to exercise when a species is transferred by our own choice from one country to another, I say by our choice, for, whether we wish it or not, certain plants will introduce themselves. In these days of frequent and intimate intercommunication between different countries, the exclusion of foreign plants is simply impossible. Our common weeds are striking illustrations of the readiness with which plants of one country 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 hawkweed, 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 Anacliaris, or Elodea, is, so far as I 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 unmitigated nuisance that it was called a curse. Efforts to extirpate it merely increased its rate of growth. Its days of mischief are, however, 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