the occurrence of identical species in distant parts of the 

 world, would favour the view that countries with similar 

 climates had originally many species of plants in common. 

 In the case of grasses, we would naturally suppose that 

 they must have been produced in their social state, 

 forming pasture for the nourishment of animals ; and such 

 we might conjecture to be the case with social plants in 

 general. 



' Edward Forbes advocates strongly the view of specific 

 centres, and endeavours to account for the isolation of cer- 

 tain species or assemblages of plants from their centres, by 

 supposing that these outposts were formerly connected, and 

 have been separated, by geological changes, accompanied 

 with the elevation and depression of land. Schouw opposes 

 this. He thinks that the existence of the same species in 

 far distant countries is not to be accounted for on the sup- 

 position of a single centre for each species. The usual 

 means of transport, and even the changes which have 

 taken place by volcanic and other causes are inadequate, 

 he thinks, to explain why many species are common to 

 the Alps and the Pyrenees on the one hand, and to the 

 Scandinavian and Scotch mountains on the other, without 

 being found on the intermediate plains and hills ; why 

 the flora of Iceland is nearly identical with that of the 

 Scandinavian mountains ; why Europe and North America, 

 especially the northern parts, have various plants in 

 common, which have not been communicated by human 

 aids. Still greater objections to this mode of explanation, 

 he thinks, are founded on the fact that there are plants at 

 the Straits of Magalhaens, and in the Falkland and other 

 antarctic islands, which belong to the flora of the Arctic 

 pole ; and that several European plants appear in New 

 Holland, Van Diemen's Land, and New Zealand, and 

 which are not found in intermediate countries. Schouw, 

 therefore, supposes that there were originally not one, but 

 many primary individuals of a species/ 



A writer in the Scotsman has called attention to the 



