50 DOUBTFUL SPECIES. Chap. II. 



that most careful observer Gartner, they can be crossed 

 only with much difficulty. We could hardly wish for 

 better evidence of the two forms being specifically dis- 

 tinct. On the other hand, they are united by many 

 intermediate links, and it is very doubtful whether these 

 links are hybrids ; and there is, as it seems to me, an 

 overwhelming amount of experimental evidence, show- 

 ing that they descend from common parents, and con- 

 sequently must be ranked as varieties. 



Close investigation, in most cases, will bring naturalists 

 to an agreement how to rank doubtful forms. Yet it 

 must be confessed, that it is in the best-known countries 

 that we find the greatest number of forms of doubtful 

 value. I have been struck with the fact, that if any 

 animal or plant in a state of nature be highly useful 

 to man, or from any cause closely attract his attention, 

 varieties of it will almost universally be found recorded. 

 These varieties, moreover, will be often ranked by some 

 authors as species. Look at the common oak, how 

 closely it has been studied ; yet a German author 

 makes more than a dozen species out of forms, which 

 are very generally considered as varieties ; and in this 

 country the highest botanical authorities and practical 

 men can be quoted to show that the sessile and pedun- 

 culated oaks are either good and distinct species or 

 mere varieties. 



When a young naturalist commences the study of a 

 group of organisms quite unknown to him, he is at first 

 much perplexed to determine what differences to consider 

 as specific, and what as varieties ; 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 



