336 Review of Hooker's Outlines 



Asiatic arctic types to their own peculiar longitudinal zones, and 

 for what is a far greater difficulty, the representation of the same 

 arctic genera by closely allied species in diflferent longitudes.* * * 

 Mr. Darwin's hypothesis accounts for many varieties of one plant 

 being found in various alpine and arctic regions of the globe, by 

 the competition into which their common ancestor was brought 

 with the aborigines of the countries it invaded. Diflferent races 

 survived the struggle for life in different longitudes ; and these 

 Taces again, afterwards converging on the zone from which their 

 ancestor started, present there a plexus of closely allied but more 

 or less distinct varieties, or even species, whose geographical limits 

 overlap, and whose members, very probably, occasionally breed 

 together." A further advantage claimed for this hypothesis is, 

 that it explains a fact brought out by Dr. Hooker in a former pub- 

 lication, viz. : " that the Scandinavian flora is present in every 

 latitude of the globe, and is the only one that is so.' 



* Moreover, Dr. Hooker, discovers in the flora of Greenland a 

 state of things explicable upon this hypothesis, but hardly by any 

 other, viz. : its almost complete identity with that of Lapland; 

 its general paucity, as well as its poverty in peculiar species ; the 

 rarity of American species there ; the fewness of temperate 

 plants in temperate Greenland ; and the presence of a few of the 

 rarest Greenland and Scandinavian species in enormously remote 

 alpine localities of West America and the United States. Our 

 author reasons thus : " If it be granted that the polar area was 

 once^occupied by the Scandinavian flora, and that the cold of the 

 glacial epoch did drive this vegetation southwards, it is evident 

 that the Greenland individuals, from being confined to a peninsu- 

 la,!would have been exposed to very different conditions from those 

 of the'great continents. In Greenland many species would, as it 

 were, be driven, into the sea, that is, exterminated ; and the sur- 

 vivors would be confined to the southern portion of the peninsula, 

 and, not being there brought into competition with other types, 

 there could be no struggle for life amongst their progeny, and, 

 consequently, no selection of better adapted varieties. On the 

 return of heat survivors would simply travel northwards, unaccom- 

 panied by^the plants of any other country.' 



* The rustic denizens of Greenland, huddled upon the point of 

 the peninsula during the long glacial cold, have never enjoyed 

 the advantages of foreign travel ; those of the adjacent continents 

 on either side have * seen the world,' and gained much improve- 



