1890.] The Distribution of Plants. 825 
treme southern portion of the American continent, and subsequent 
study brought out a far greater extension of this relationship. 
A further interesting observation was that the plants of the 
Antarctic Islands that are also natives of Tasmania, New Zeal- 
and, and South America, are almost invariably found only on the 
lofty mountains of those countries. 
In view of these and other results, Dr. Hooker was strongly 
impressed with the view that existing agencies are not sufficient 
to account for the observed facts, and concludes that these floras 
— * exhibit a botanical relationship as strong as that which prevails 
throughout the land within the Arctic and Northern Temperate 
zones, and which is not to be accounted for by any theory of 
transport or variation, but which is agreeable to the hypothesis 
of all being members “of a once more extensive flora, which has 
been broken up by geological and climatic causes.” 
In the “Outlines of the Distribution of Arctic Plants,” pub- 
lished in 1861, an attempt was made to trace the distribution of 
every phanogamous species known to occur spontaneously 
within the Arctic circle. The distinctively Scandinavian char- 
acter of the Arctic flora, the remarkable deficiency of Greenland 
in characteristically American species, and the fact that no close 
‚relation was discovered between the isothermal lines and the 
amount of vegetation, so that the observed facts remained to be 
accounted for in some other way than by reference to present 
climatic conditions, were some of the most important results of 
this study. The explanation offered involved the two principles 
already established by Dr. Gray, viz., the community of origin of 
closely related species, and forced migrations under the influence 
of climatic changes. 
The results of Dr. Hooker's study of insular floras were em- 
bodied in a paper presented to the British Association at its Not- 
tingham meeting in 1866.” It contained the most extended 
account that has yet been given of island life from the strictly 
botanical point at a view- The dii emphasizes the fact that the 
flora of no tand sui generis, butis always 
very manifestly allied to some > continental flora; but that they all 
12 Translated in the Ans. des Sci. Nat., Ser. V., Tom. 6. 
