CHAPTER II 



THE DISPERSAL OF PLANTS INTO 

 NEW AREAS 



A \TERY large number of species are to be found at more or less 

 frequent intervals over enormous areas of territory, often in 

 regions separated by large stretches of water, or sometimes of . 

 land. Never, since the days of the hypothesis of special creation, 

 has it been maintained that a species originally arose over the 

 whole of the area upon which it now occurs. This would be a 

 difficult proposition to uphold, as it is usually found that when 

 a species occupies a large territory, it has different varieties in 

 different parts. Various views, however, have at times held sway 

 as to the probable extent of the land surface upon which a 

 species began, Darwin (22, in, 109), for example, had at one time 

 the idea that it might arise under Natural Selection from one or 

 a few individuals varying in the desired direction, but Fleeming 

 Jenkin brought up a criticism of this position so incisive that 

 he was forced to abandon it, and postulate for a much more 

 numerous original ancestry, of course occupying a much larger 

 amount of ground. It is perhaps from this latter position taken 

 up by him that the current view has arisen, according to which 

 species that now occupy very small areas of country owe the 

 smallness of that area to the supposed fact that they are really 

 in process of dying out, for they could not have arisen by aid 

 of the Darwinian mechanism of Natural Selection upon so small 

 a space. 



At the present time, however, when this mechanism of in- 

 finitesimal variation with natural selection (or survival of the 

 fittest) is not commonly accepted as being the principal factor 

 in the production of new species, it is probable that comparatively 

 few people would be found to demand more than a relatively 

 limited area for the purpose. Not many, perhaps, have any 

 exact idea of how much would be needed, but possibly the 

 majority would require either a little more than just a few 

 square yards, or the repeated origin of the same species upon 

 the same area. A good many writers, both of former times and 

 of the present, have adopted the view that it is not absolutely 



