8 



independent of him for existence, come Tinder the c.itetrory of 

 naturalized plants. The buttercup, eli'ver, Canada thisth; and 

 sheep sorrel, 8trikiiii>ly exemplify this extensive group. 



The remainini^ groups re(|uire a more attentive consideration. 

 All of the species referred to them are indigenous to tliis c<uintry ; 

 some to tlie settled, otluTS to the remote districts. \\ ith many 

 individual plants of sduie of the species it forms a question 

 whether their introduced habit indicates a foreign origin or results 

 from a tendency of the indigenous plant to abiionnally spuad. 

 In certain in.^tanccs the known limited di.'«triliution of the species, 

 in its indigenous form, dispels any doubt. For ex;im[)le, around 

 Lake Superior. Agassiz chronicles as native, or ])robably .so, 

 species who.se habits, in the settled parts of the country, evince a 

 decidedly exotic origin. AVliere, however, the range of both forms 

 is extensive, indicating the limits of each is imiiractieable. It is 

 indeed pomble that not only have the rambles of the n;iiive species 

 frefpiently placed them side by side with the domesticated plants, 

 and probably (juite undistinguishable from them, but that in some 

 instances the species, though common to Europe .ind America, 

 have no introduced representatives here; and that individuals of 

 these species, which have the habits of exotics, are in reality 

 indigenes which have wandered beyond their natural homes. 



A (jue^tion, replete with interest, arises in connection with 

 these naturalized plants. Have changes <if climate and of other 

 conditions in the long lapse of years impres,><ed new spicific cliar- 

 acters on the individuals of any .species, or, if not, have they pro- 

 duced any permanent varieties'? If even the latter were tlu^ ease, 

 it seems probable that not oidy might varieties be diff-rent on 

 different continents, but the migration of thest- varieties might also 

 lead to s{)eciiic cluuiges. Let the imagination trace the wander- 

 ings of one of these little plants under such circumstances. 

 I'robably of a spreading habit in its native country, it ('migrates, 

 th»-ough one of the imiumerable channels constantly op^n, to a 

 foreign clime, where it becomes establislied, and where, in conse- 

 quence of a change of conditions, .some slight but pi'rmanent 

 alteration is effected in its characters. The plant thrives, and ii» 

 the lapse of years biconus a widely distributeil weeil. Anotlur 

 emigration takes place thence to a country where climatal and 

 other conditions are different from tho}.c of either its luitive country 

 or last adopted home. A nmre marked variety results. In the 

 course of long time this variety appears on another continent, to 



