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The numerous facts we have already given, and many others that might be arrayed in advocacy of our position, taken in connection with the general facts here presented in regard to plant-distribution, all point directly to climatal and soil conditions as the real cause of dissemination, and not to their migration from continent to continent, and across vast intervening seas and oceans, as the theory of Professor Gray and others would require us to believe.
As exemplifying the effects of climatal changes on distribution, I have attempted to show how important has been the influence of the modern Glacial period, which I am fully convinced simultaneously affected the whole world, or at least great meridional belts.
The process of diffusion may often be very slow, being dependent on climatal and geographical changes, or on strange accidents, but in the long run the dominant forms will generally succeed in spreading. The diffusion would, it is probable, be slower with the terrestrial inhabitants of distinct continents than with the marine inhabitants of the continuous sea.
It is further to be noted and this is a very interesting point in connection with theories of the dependence of special forms of life on external conditions that this division of the Archipelago into two regions characterised by a striking diversity in their natural productions does not in any way correspond to the main physical or climatal divisions of the surface.
If these faculties are so much enfeebled as to be irrecoverable it will perish; if not and if it can adapt itself to the surrounding conditions, it will revert to the state in which Man first found it: for in one, two, or three thousand years, which may have elapsed since it was originally tamed, there will not have been time for such geographical, climatal, and organic changes as would only be suited to a new race or a new and allied species.
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