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WOELD. 283 



e 



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1 



I 





I 



of varieties between tlie terms of which no hiatus exists such 



intercalation of any intermediate 



as might allow of the 



variety. The genera Eubus, Eosa^ Salix^ and 

 afford conspicuous examples of these unstable forms ; Ve- 

 ronica^ Campanula^ and Lobelia of comparatively stable ones. 

 At the same time he j)oints out in accordance with Mr. 

 Darwin's theory how the extinction of a certain number of 

 the intermediate races by destroying the transitional links, 

 would facilitate the classification of the remaining species, 

 and hints that we may be indebted to such extinction in 

 past times for whatever facility we now enjoy of resolving 



plants into distinct species, genera, and orders. ^The mutual 

 relations,' he observes, ' of the plants of each great botanical 

 province, and in fact, of the world generally, is just such as 

 would have resulted if variation had gone on operating- 



throughout indefinite periods, in the same manner as we see 

 it act in a limited number of centuries, so as gradually to 

 give rise in the course of time to the most widely divergent 

 forms.' 



we reflect that this statement was made after a 



When 



study of the characters and geographical distribution of tens 

 of thousands of species, we feel disposed at once to declare 

 that a theory which is in harmony with so many facts must 

 be true ; but if so, we have to enquire how it happens that so 

 many naturalists, of undoubted ability and knowledge, have 

 always held and still believe that species have been constant 

 from the beginning. In reference to this question, Dr. 

 Hooker admits that species are realities and may be treated 

 as if they were permanent and immutable ; for the forms and 

 characters, at least of the great majority of them, may be 

 faithfully transmitted through thousands of generations, and 



remained 



ence. 

 it will 



remarks, ^ is so limited 



not account for a single fact in the 



present geo- 

 graphical distribution, or origin of any one species of plant, 



amount 



i=3 



time when it first anneared nor the form 



had when created.' ^ 



^ Hooker, Introductory Essay, Flora of Tasmania. 



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