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but unluckily these are comparatively few, and it is a notable fact that, 

 although so many species of our common aggressive weeds have come to 

 us from Europe, very few from this side have held their own in the old 

 world. A partial reason for this may be that up to this time much 

 more seed has been brought here from Europe for farms and gardens 

 than has been sent back from this side. Dr. Gray's theory, however, 

 is probably the correct one, and it accounts for the large proportion of the 

 European introduced plants becoming so objectionable here. He points 

 out that, up to a quite recent date, our whole country was covered with 

 forests, and consequently all the indigenous plants would be forest 

 plants. It is apparent, therefore, that for this reason they woidd be 

 unsuited to live in the open spaces when cleai-ed. On the other hand 

 the hardy European ragamuffins used to pick up a scanty living among 

 flag-stones and upon rubbish heaps, would grow apace when introduced 

 into our lich virgin soil, where there were no rivals to oppose them; 

 thus it is merely a phase of the old story — the survival of the fittest. 

 Of course this argument would also apply to seeds accidentally taken to 

 Europe; they would be unable to survive without the constant supply 

 of moisture in the atmosphere which, through many generations, they 

 had been used to in their native forest. This leads us to another theory 

 viz. : that one so ably advocated before the Royal Society of Canada, 

 by Prof. Macoun, to the effect that the humidity of the atmosphere is 

 the chief element which aff'ects the distribution of the diff'erent species 

 of plants. Prof. Claypole (Rep. 3, Mont. Hort. Soc.) argues very 

 elaborately, and possibly with some reason, that the types of vegetation 

 in Europe are of a more plastic nature than those of this continent, from 

 having had, during a long ]jeriod, to live under very varying circum- 

 stances, and to adapt themselves to many diflferent changes of habitat. 

 In support of this theory he points out that the fossil Floras of Europe 

 and the American of to-day, are very closely allied. He cites some very 

 remarkable instances of Tertiary and Miocene plants, almost identical 

 with existing American forms, and infers that the type of vegetation 

 which we have here now, once existed in Europe as well ; but from a 

 lack of plasticity failed to survive. This theory may be partially true, 

 but I think that the humidity of the atmosphere, namely the nature of 

 the habitat, is the chief cause. If it were not the habitat which chiefly 



