POSSIBILITIES OF ECONOMIC BOTANY. 217 



duction of useful plants into Australasia have been aided largely 

 by bis 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 be- 

 tween 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, f 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 draw- 

 ing 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 



* See note, p. 59. 



f The weeds of German gardens and agricultural lands are mostly from Mediterranean 

 regions, but the invasions in the uncultivated districts are chiefly from America (such as 

 (Enothcra^ MimuJus, Ricdheckia). Handbuch der PJlanzengeograpJiie, von Dr. Oscar 

 Drude (Stuttgart), 1890, p. 97. 



