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Sit 



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w 





sei 



u 



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 ■'intlf 



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mn 



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to tie 



1 



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Jbf 



fi- 



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Ch. XL.] 



MIGEATION OF SPECIES. 



399 



^ 



west reo'iou of America, lias now established itself in various 

 parts of England, and is spreading- rapidly. 



In hot and ill-cultivated countries, such naturalisations 

 take place more easilj. Thus the Chenopodium amhrosioides, 

 sown by Mr. Burchell on a point of St. Helena, multiplied so 

 fast in four years as to become one of the commonest weeds 

 in the island, and it has maintained its ground ever since 



1845. 



The most remarkable proof, says De CandoUe, of the extent 



to which man is unconsciously the instrument of dispersing 

 and naturalising species, is found in tlie fact, that in New 

 Holland, America, and tlieCape of Good Hope, tlie European 

 species exceed in number all the others which have come from 

 any distant regions ; so that, in this instance, the influence of 

 man has surpassed that of all the other causes which tend to 

 disperse plants over remote regions, 

 British flowering plants are supposed to be naturalised 

 species, and a large proportion of them would ]3erish with the 

 discontinuance of agriculture. 



Although we are but slightlj acquainted, as yet, with the 

 extent of our instrumentality in naturalising species, yet the 

 facts ascertained afford no small reason to suspect that the 

 number which we introduce unintentionally exceeds all those 

 transported by design. Nor is it unnatural to suppose that 

 the functions, which the inferior beings extirpated by man 



About a fifth of the 



once 



discharged in the economy of nature, should devolve 



human 



many 



'o 



from diflerent countries, Ave are probably required to fulfil their 

 office of carrying seeds, eggs of fish, insects, moUusks, and 

 other creatures, to distant regions : if we extirpate quadrupeds, 

 we must replace them not merely as consumers of the animal 

 and vegetable substances which they devoured, but as disse- 

 minators of plants, and of the inferior classes of the animal king- 

 dom. I rlmin+, mpnn fn ir»«iTinn,+,A fhp+. +,TiP vAr\ 



same 



man 



mer 



number 



* Principles of Botany, p. 389 



f * 



