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these connecting links may very possibly be destroyed, and 

 hence the detached portions of the land, which still stand 

 up above the level of the ocean, would present only those 

 varieties which are too far removed one from the other to 

 be recognized as belonging to the same type. Under these 

 circumstances it is quite conceivable that the form most 

 common at the present day might not be the typical one, 

 but only one of many varieties which were superinduced by 

 differences in external conditions. 



Their prevalence at the present time may by no means 

 imply that they were the predominant forms originally; 

 since it is quite possible that subsequent geological cata- 

 strophes should have swept away those parts of the con- 

 tinent where the typical form had been developed. 



Hence Dr. Hooker contends, there is no absurdity in 

 supposing trees so different as the Deodar and the Cedar of 

 Lebanon to be modifications of the same species. The great 

 variations in form which occur in the latter tree when in- 

 troduced into England, and the approach which some spe- 

 cimens of it make to the Cedars of the Atlas on the one 

 hand and to the Deodar Cedars on the other, lead him to 

 suspect that those which now grow on the Mountains of 

 Lebanon belong only to an abnormal form of the species, 



