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9 



i 



Ch. XXXVII.] 



DE CANDOLLE'S OPINIONS. 



525 



ingenious papers on mule plants^ endeavours to account for 



^ 



t) 



guments 



then' rare occurrence m a state 01 nature^ irom the circum- 

 stance that all the combinations that Avere likely to occur 

 have already been made many centuries ago; but in our 

 gardens^ he says, whenever species, having a certain degree 

 of affinity to each other, are transported from different coun- 

 tries, and brought for the iirst time into contact, they give 

 rise to hybrid species. 



De CandoUe^s opinions. — Auguste De CandoUe, in his Essay 

 on Botanical Geography, published in 1820, observes, that 

 the varieties of plants range themselves under two general 

 heads : those produced by external circumstances, and those 

 formed by hybridity. 

 show that neither of these causes can explain the permanent 

 diversity of plants indigenous in different regions, he says, in 

 regard to the crossing of races, ' I can perfectly comprehend, 

 without altogether sharing the opinion, that, where many 

 species of the same genera occur near together, hybrid species 

 may be formed, and I am aware that the great number of 

 sjoecies of certain genera which are found in particular regions 

 may be explained in this manner; but I am unable to conceive 

 how anyone can regard the same explanation as applicable to 

 species which live naturally at great distances. If the three 

 larches, for example, now known in the Avorld, lived in the 

 same localities, I might then believe that one of them was the 

 produce of the crossing of the two others ; but I never could 

 admit that the Siberian species has been produced by the 

 crossing of those of Europe and America. I see, then, that 

 there exist, in organised beings, permanent differences which 

 cannot be referred to any one of the actual causes of varia- 

 tion, and these differences are Avhat constitute species.' f In 

 this passage De CandoUe assumes that the actual causes of 



limits 



transmutation 



reason, is quite as arbitrary as the opposite or rival assump- 

 tion of indefinite modifiability. 

 - Hyhridity will not account for special instincts. -As to the 



^^ Hon. and Eev. W. Herbert, Hort. Trans., vol. iv. p. 41. 



t Essai Elemcntaire, &e. 3ieme partie. 





-_ 1 j 



v 



