138 REVIEWS. 



show that the idea and the practical application of the term 

 species have remained unchanged during the century which 

 has elapsed since the publication of the "Species Plantarmn." 

 But the idea remaining unchanged, the facts might appear 

 under a different aspect, and the conclusion be different, un- 

 der a slight and very supposable change of circumstances. Of 

 the twenty-eight spontaneous varieties of Q. Itobur, which 

 De Candolle recognizes, all but six, he remarks, fall naturally 

 under the three sub-species, jyechinadata, sessiliflora, and 

 jiubescens, 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 fre- 

 quently taken for species, would be what the group of four 

 or five provisionally admitted species which closely surround 

 Q. Robur (see p. 435) now are. The best example of such 

 a case, as having in all probability occurred, through geo- 

 graphical segregation and partial extinction, is that of the 

 Cedar, thus separated into the Deodar, the Lebanon, and the 

 Atlantic Cedars, — a case admirably worked out by Dr. 

 Hooker two or three years ago. 1 



A special advantage of the Cupuliferce for determining 

 the probable antiquity of existing species in Europe, De Can- 

 dolle 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 establishment of 

 a forest of Oaks or Chestnuts in this way, De Candolle con- 

 ceives to be fairly impossible in itself, and contrary to all 

 experience. From such considerations, 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 prin- 

 cipal Cupvliferce of the Old World attained their actual ex- 

 tension before the pi*esent separation of Sicily, Sardinia and 

 Corsica, or of P>ritain, from the European continent. 

 1 Natural History Review, Jan., 18G2. 



