DOUBTFUL SPECIES 67 



species are in a feeble minority. This seemed to be true, so 

 long as a genus was imperfectly known, and its species were 

 founded upon a few specimens, that is to say, were pro- 

 visional. Just as we come to know them better, intermediate 

 forms flow in, and doubts as to specific limits augment." He 

 also adds that it is the best known species which present the 

 greatest number of spontaneous varieties and sub-varieties. 

 The Quercus robur has twenty-eight varieties, all of which, 

 excepting six, are clustered round three sub-species, namely, 

 Q. pedunculata sessiliflora, and pubescens. The forms which 

 connect these three sub-species are comparatively rare; and, 

 as Asa Gray again remarks, if these connecting forms which 

 are now rare, were to become wholly extinct, the three sub- 

 species would hold exactly the same relation to each other, as 

 do tlie four or five provisionally admitted species which 

 closely surround the typical Quercus robur. Finally. De 

 Candolle admits that out of the 300 species, which will be 

 enumerated in his Prodromus as belonging to the oak family, 

 at least two-thirds are provisional species, that is, are not 

 known strictly to fulfil the definition above given of a true 

 species. It should be added that De Candolle no longer be- 

 lieves that species are immutable creations, but concludes 

 that the derivative theory is the most natural one, "and the 

 most accordant with the known facts in palaeontology, geo- 

 graphical botany and zoology, of anatomical structure and 

 classification." 



When a young naturalist commences the study of a group 

 of organisms quite unknown to him, he is at first much per- 

 plexed in determining what differences to consider as specific, 

 and what as varietal; for he knows nothing of the amount 

 and kind of variation to which the group is subject; and this 

 shows, at least, how very generally there is some variation. 

 But if he confine his attention to one class within one country, 

 he will soon make up his mind how to rank most of the doubt- 

 ful forms. His general tendency will be to make many 

 species, for he will become impressed, just like the pigeon or 

 poultry fancier before alluded to, with the amount of differ- 

 ence in the forms which he is continually studying; and he 

 has little general knowledge of analogical variation in other 

 groups and in other countries, by which to correct his first 



