Variation, Geographical Distribution, and Succession. 87 



have regarded it as including three species, Q. pedunculata, Q. 

 sessiliflora, and Q. pubescens. DeCandolle looks with satisfaction 

 to the independent conclusion which he reached from a long 

 and patient study of the forms (and which Webb, Gay, Bentham, 

 and others had equally reached), that the view of Linnseus was 

 correct, inasmuch as it goes to show that the idea and the prac- 

 tical application of the term species have remained unchanged 

 during the century which has elapsed since the publication of 

 the ' Species Plantarum.' But, the idea remaining unchanged, 

 the facts might appear under a different aspect, and the conclu- 

 sion be different, under a slight and very supposable change of 

 circumstances. Of the twenty-eight spontaneous varieties of 

 Q. robur which DeCandolle recognizes, all but six, he remarks, 

 fall naturally under the three subspecies, pedunculata, sessiliflora, 

 and 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 (see p. 85) 

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

 probability occurred through geographical segregation and par- 

 tial 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*. 



A special advantage of the Cupulifera for determining the 

 probable antiquity of existing species in Europe, DeCandolle 

 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 ail 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), DeCandolle conceives to be fairly impos- 

 sible in itself, and contrary to all experience. From such con- 

 siderations, i. e. from the actual dispersion of the existing spe- 

 cies, with occasional aid from Post-tertiary deposits, it is thought 

 to be shown that the principal Cupuliferce of the Old World at- 

 tained their actual extension before the present separation of 

 Sicily, Sardinia, and Corsica, or of Britain, from the European 

 continent. 



This view once adopted, and this course once entered upon, 

 has to be pursued further. Quercus robur of Europe, with its 



* Nat. Hist. Review, January 1862 ; see Sillimann's Journal, ser. 2. 

 vol. xxiv. p. 148. 



