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there was no further opportunity afforded for the diffusion by 

 natural means of any other floral type, or of any other new 

 species of plants from these into our islands. And here, 

 could we possibly determine with accuracy what plants were thus 

 and then introduced, we would have the only adequate solution 

 of the much vexata questio amongst botanists, as to what really 

 constitute our native versus our naturalised species. The 

 theory thus briefly stated, and illustrated at some length in the 

 case of our alpine flora, will, as we have said, be found to hold 

 good also with respect to our cryptogammic flora, which Forbes 

 does not notice. From the uncertainty, however, as to the dis- 

 tribution of some orders of these, such as the fungi, we have, as 

 yet, been able fully to work it out only in the mosses and lichens. 

 Moreover it is applicable, as may readily be inferred, not only to 

 the flora of our own, but to that of any other country, and the 

 more we have examined the grounds upon which it rests, and the 

 proofs by which it may be supported, the stronger these have 

 been felt to be and the better its claims to our acceptance. 

 Starting, with the geological relations of plants as enunciated 

 in this theory, the geographical botanist is in a much better 

 position to estimate the various influences exerted by climate, 

 habitat, soil, and such like, in regulating their subsequent distri- 

 bution over the several countries of the globe. 



