ON Tili^ ( I1AI!ACTE11I!<TICS» Ol" Tllli NOUllI AMEUICAN FLORA. 



563 



that there arc good species which T had reckoned as aynonymH, and some 

 that luay rise to arboreal height which I had counted as shmbs. But, on 

 the other hand, and for the present purpose, it may bo rejoined that, the 

 list contained several ti-ees, of as many genera, which were probably 

 carried from Asia into Europe by the hand of man. Ou Nymau's authority 

 I may put into this category cercis siliipiastrum, coratonia Biliqna, 

 diospyros lotus, styrax oflicinalis, the olive, and even the walnut, tho 

 cliLstnut, and tho cypress. However this may he, it seems clear that the 

 iiutive forest ilora of Kurope is exceptionally poor, and that it has lost 

 many species and typos which onci; belongLcl to it. Wo nuist suppose 

 that the herbaceous iloni has suH'orcd in tho same way. 1 have en- 

 deavoured to show how this has naturally come about. I cannot state it 

 more concisely than in tho terms which I used six years ago. 



' 1 conceive that three things have conspired to this loss of American, 

 or, as we might say, of normal, types sustained by Kurope. I'^irst, Europe, 

 extending but littlo south of hit. io ', is all within the limits of sovero 

 glacial action. Second, iis mountains trend east and west, from the 

 Pyrenees to tho Carpathians and the Caucasus beyond : they had glaciers 

 of their own, which must have begun their work and poured down the 

 northward flanks while the plains were still covered with forest on tho 

 retreat from the great ice forces coming from the north. Attacked both 

 on front and rear, much of the forest must have perished then and 

 there. 



• Third, across the lino of retreat of whatever trees may have flanked 

 tlu' mountain ranges, or were stationed south of them, stretched the 

 ^Mediterranean, an impassable barrier. . . Escape by the cast, and rehabi- 

 litation from that quarter until a very late period, was apparently prevented 

 by the prolongption of the Mediterranean to the Caspian, and probably 

 thence to the Siberian Ocean. If we accept the supposition of Norden- 

 skiokl that, anterior to the Glacial ])eriod, Europe was "bounded ou the 

 south by an ocean extending from tlie Atlantic over the present deserts of 

 Sahara and Central Asia to the Pacific," all chance of these American 

 types having escaped from and re-entered Europe from the south and east 

 seems excluded. Europe may thus be conceived to have been for a time 

 somewhat in tho condition in which (Ireenland is now. . . . Greenland. 

 may be referred to as a country which, having undergone extreme 

 glaeiation, bears the marks of it in tho extreme poverty of its flora, and 

 in the absence of tho plants to which its southern portion, extending six 

 degrees below the arctic circle, might be entitled. It ought to have trees, 

 and it might support them. But since their destruction by glaeiation no 

 way has been open for their return. Europe fared much better, but has 

 suffered in its degree in a similar way.'' 



Turning to this country for a contrast, we find the continent on the 

 eastern side unbroken and open from the arctic circle to the tropic, and 

 the mountains runuinj;- north and south. The vegetation when pressed 

 on the north by on-coming refrigeration had only to move its southern 

 border southward to enjoy its normal climate over a favourable region of 

 gi'eat extent ; and, upon the recession of glaeiation to the present limit, or 

 in the oscillations which intervened, there was no physical impediment 

 to the adjustment. Then, too, tho more southern latitude of this country 

 gave great advantage o\er Europe. The line of terminal moraines, which 



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