88 DOUBTFUL SPECIES. [CHAP. H. 



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 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 classification." 



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 varia- 

 tion 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 

 tendency will be to make many species, for he will become im- 

 pressed, 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 varia- 

 tion 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 observations 

 be widely extended, he will in the end generally be able to make 

 up his own mind : but he will succeed in this at the expense of 

 admitting much variation, and the truth of this admission will 

 often be disputed by other naturalists. When he comes to study 

 allied forms brought from countries not now continuous, in which 

 case he cannot hope to find intermediate links, he will be com- 

 pelled to trust almost entirely to analogy, and his difficulties will 

 rise to a climax. 



Certainly no clear line of demarcation has as yet been drawn 

 between species and sub-species that is, the forms which in the 

 opinion of some naturalists come very near to, but do not quite 

 arrive at, the rank of species : or, again, between sub-species and 

 well-marked varieties, or between lesser varieties and individual 

 differences. These differences blend into each other by an insen- 

 sible series ; and a series impresses the mind with the idea of an 

 actual passage. 



Hence I look at individual differences, though of small interest 

 to the systematist, as of the highest importance for us, as being 

 the first steps towards such slight varieties as are barely thought 

 worth recording in works on natural history. And I look at 

 varieties which are in any degree more distinct and permanent, 



