422 BOTANICAL GEOGRAPHY. 



Since the Alps contain so many alpine species in common with the arctic 

 regions, it is still more easily seen how little the continent situated between 

 these two terminal points serves to explain these agreements. The plains 

 which, without this alpine attire, extend e. g. from Cola to the Carpathians, 

 are, however, less adapted to the transport of foreign plants than a sea which 

 rapidly carries over the seeds in its current. Or when Forbes has recourse 

 to the glacial period in explaining the diffusion of the arctic plants : how 

 will he account for so many central European species of Sierra Nevada or 

 Pindus traversing the extensive tracts of land which separate them from 

 their centre of creation ? How, by the most complex dislocations, will he 

 bring the Minuartice and Queritf into geological connexion, which do not 

 nourish anywhere between Castile and the Crimea? There is no reason 

 why water should form a greater obstacle to the distribution of plants than a 

 soil which does not conduct them ; extensive oceans certainly form barriers, 

 when there is no current to carry them across, or when the climates of the 

 two coasts are dissimilar. 



A. Erman has written a paper on the periods of vege- 

 tation in different climates (Arch, fur Russian d, Bd. 5, 

 pp. 617-40). 



He examines the question, of what relation the stages of development 

 of vegetation hold to the temperature, at which in different latitudes they 

 appear in the same species. His investigations lead to the negative result, 

 that a law communicated to him conjecturally by Quetelet is unfounded. 

 It consisted in the assumption that similar stages of development occur in 

 two different places, when the sum of the squares of the diurnal temperature 

 from the commencement of the period of vegetation is the same for both. He 

 shows, also, that the stages of development and the sum of the temperature 

 acting upon them in different places, are by no means in direct proportion. 



We must mention a remark made by J. D. Hooker in 

 regard to botanico-geographical physiognomy (On Fitchia, 

 in Lond. Journ. of Bot., 1845, p. 640). 



On many remote islands possessing endemic floras, we find woody plants 

 belonging to the family of Synantheracese, which contribute essentially to 

 the character of the districts, and belong to peculiar genera, of which re- 

 presentatives do not occur on the continents. The following sketch will 

 serve to illustrate this : 



St. Helena contains 4 gen. 10 sp. of Synantheracea?, all woody plants ; 

 Juan Fernandez 8 17 of of which 3 gen. and 



12 sp. are woody plants ; 

 Gallapagos contains 13 gen. 21 sp. of Synantheraceae, of which 3 gen. and 



8 sp. are woody plants ; 



New Zealand contains 30 gen. 60 sp. of Synautheracea3, of which 8 gen. 

 and 14 sp. are woody plants. 



