NORTH AMERICAN FLORA. 261 



lines of the vegetation of the United States and the Canadian 

 Dominion, as contrasted with that of Europe ; perhaps also to 

 touch upon the causes or anterior conditions to which much 

 of the actual differences between the two floras may be as- 

 cribed. For, indeed, however interesting or curious the facts 

 of the case may be in themselves, they become far more in- 

 structive when we attain to some clear conception of fche de- 

 pendent relation of the present vegetation to a preceding state 

 of things, out of which it has conic 



As to the Atlantic border on which we stand, probably the 

 first impression made upon the botanist or other observer coin- 

 ing from Great Britain to New England or Canadian shores, 

 will be the similarity of what he here finds with what he left 

 behind. Among the trees the White Birch and the Chestnut 

 will be identified, if not as exactly the same, yet with only 

 slight differences — differences which may be said to be no 

 more essential or profound than those in accent and intona- 

 tion between the British speech and that of the k ' Americans/* 

 The differences between the Beeches and Larches of the two 

 countries are a little more accentuated; and still more those 

 of the Hornbeams, Elms, and the nearest resembling Oaks. 

 And so of several other trees. Only as you proceed westward 

 and southward will the differences overpower the similarities, 

 which still are met with. 



In the fields and along open roadsides the likeness seems 

 to be greater. But much of this likeness is the unconscious 

 work of man, rather than of Nature, the reason of which is 

 not far to seek. This was a region of forest, upon which the 

 aborigines, although they here and there opened patches of 

 land for cultivation, had made no permanent encroachment 

 Not very much of the herbaceous or other low undergrowth 

 of this forest could bear exposure to the fervid summer's sun ; 

 and the change was too abrupt for adaptive modification. The 

 plains and prairies of the great Mississippi Valley were then 

 too remote for their vegetation to compete for the vacancy 

 which was made here when forest was changed to grain-fields 

 and then to meadow and pasture. And so the vacancy came 

 to be filled in a notable measure by agrestial plants from En- 



