308 Geographical Distribution of Plants 



thought singular that he should have been elected a "correspondant" 

 of the Academic des Sciences in the section of Botany, but it is not 

 surprising that his work in Geographical Botany made the botanists 

 anxious to claim him. His heart went with them. " It has always 

 pleased me," he tells us, "to exalt plants in the scale of organised 

 beings 1 ." And he declares that he finds " any proposition more easily 

 tested in botanical works 2 than in zoological." 



In the Introductory Essay Hooker dwelt on the "continuous 

 current of vegetation from Scandinavia to Tasmania 3 ," but finds 

 little evidence of one in the reverse direction. " In the New World, 

 Arctic, Scandinavian, and North American genera and species are 

 continuously extended from the north to the south temperate and 

 even Antarctic zones ; but scarcely one Antarctic species, or even 

 genus advances north beyond the Gulf of Mexico 4 ." Hooker con- 

 sidered that this negatived "the idea that the Southern and Northern 

 Floras have had common origin within comparatively modern geo- 

 logical epochs 5 ." This is no doubt a correct conclusion. But it is 

 difficult to explain on Darwin's view alone, of alternating cold in 

 the two hemispheres, the preponderant migration from the north to 

 the south. He suggests, therefore, that it "is due to the greater 

 extent of land in the north and to the northern forms... having... 

 been advanced through natural selection and competition to a higher 

 stage of perfection or dominating power 6 ." The present state of the 

 Flora of New Zealand affords a striking illustration of the correctness 

 of this view. It is poor in species, numbering only some 1400, of 

 which three-fourths are endemic. They seem however quite unable 

 to resist the invasion of new comers and already 600 species of foreign 

 origin have succeeded in establishing themselves. 



If we accept the general configuration of the earth's surface as 

 permanent a continuous and progressive dispersal of species from 

 the centre to the circumference, i.e. southwards, seems inevitable. 

 If an observer were placed above a point in St George's Channel 

 from which one half of the globe was visible he would see the greatest 

 possible quantity of land spread out in a sort of stellate figure. The 

 maritime supremacy of the English race has perhaps flowed from the 

 central position of its home. That such a disposition would facilitate 

 a centrifugal migration of land organisms is at any rate obvious, and 

 fluctuating conditions of climate operating from the pole would 

 supply an effective means of propulsion. As these became more 



1 Life and Letters, i. p. 98. 2 Ibid. n. p. 99. 



3 Introductory Essay to the Flora of Taniiiania, London, 1859. Reprinted from the 

 Botany of the Antarctic Expedition, Part in., Flora of Tasmania, Vol. i. p. ciii. 



4 p. civ. 6 Loc. cit. 



6 Origin of Species (6th edit.), p. 340; cf. also Life and Letters, n. p. 142. 



