48 DOUBTFUL SPECIES. 



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. Thus 

 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 compara- 

 tively rare; and, as Asa Gray again remarks, if these con- 

 necting forms which are now rare were to become totally 

 extinct the three sub-species would hold exactly the same 

 relation to each other as do the four or five provisionally 

 admitted species which closely surround the typical Quer- 

 cus 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 provis- 

 ional 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 believes 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, geographical 

 botany and zoology, of anatomical structure and classific- 

 ation. '^ 



When a young naturalist commences the study of a 

 group of organisms quite unknown to him he is at first 

 much perplexed 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 doubtful forms. His general ten- 

 dency 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 difference 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 impressions. 

 As he extends the range of his observations he will meet 

 with more cases of difficulty; for he will encounter a 

 greater number of closely allied forms. But if his obser- 

 vations be widely extended he will in the end generally be 



