188 BARWINIANA. 



pubescens, and are therefore forms grouped around 

 these as centres ; and, moreover, the few connecting 

 forms are by no means the most common. Were 

 these to die out, it is clear that the three forms which 

 have already been so frequently taken for species 

 would be what the group of four or five provisionally 

 admitted species which closely surround Q. Robur 

 now are. The best example of such a case, as having 

 in all probability occurred through geographical segre- 

 gation and partial extinction, is that of the cedar, thus 

 separated into the Deodar, the Lebanon, and the At- 

 lantic cedars — a case admirably worked out by Dr. 

 Hooker two or three years ago. 1 



A special advantage of the Oiqndlferce for deter- 

 mining the probable antiquity of existing species in 

 Europe, De Candolle finds in the size and character of 

 their fruits. However it may be with other plants 

 (and he comes to the conclusion generally that marine 

 currents and all other means of distant transport have 

 played only a very small part in the actual dispersion 

 of species), the transport of acorns and chestnuts by 

 natural causes across an arm of the sea in a condition 

 to germinate, and much more the spontaneous estab- 

 lishment of a forest of oaks or chestnuts in this way, 

 De Candolle conceives to be fairly impossible in itself, 

 and contrary to all experience. From such considera- 

 tions, i. e., from the actual dispersion of the existing 

 species (with occasional aid from post-tertiary deposits), 

 it is thought to be shown that the principal Cupuli- 

 ferce of the Old World attained their actual extension 



1 Natural History Rcviexv, January, 1862. 



