Chap. II.] DOUBTFUL SPECIES. 57 



unite by means of intermediate links any two forms, 

 lie treats the one as a variety of the other ; ranking the 

 most common, but sometimes the one first described, as 

 the species, and the other as the variety. But cases of 

 great difficulty, which I will not here enumerate, 

 sometimes arise in deciding whether or not to rank 

 one form as a variety of another, even when they are 

 closely connected by intermediate links ; nor will the 

 commonly-assumed hybrid nature of the intermediate 

 forms always remove the difficulty. In very many cases, 

 however, one form is ranked as a variety of another, not 

 because the intermediate links have actually been 

 found, but because analogy leads the observer to 

 suppose either that they do now somewhere exist, or 

 may formerly have existed; and here a wide door for 

 the entry of doubt and conjecture is opened. 



Hence, in determining whether a form should be 

 ranked as a species or a variety, the opinion of 

 naturalists having sound judgment and wide expe- 

 rience seems the only guide to follow. We must, 

 however, in many cases, decide by a majority of 

 naturalists, for few well-marked and well-known 

 varieties can be named which have not been ranked as 

 species by at least some competent judges. 



That varieties of this doubtful nature are far from 

 uncommon cannot be disputed. Compare the several 

 floras of Great Britain, of France, or of the United 

 States, drawn up by different botanists, and see what a 

 surprising number of forms have been ranked by one- 

 botanist as good species, and by another as mere 

 varieties. Mr. H. C. Watson, to whom I lie under 

 deep obligation for assistance of all kinds, has marked 

 for me 182 British plants, which are generally con- 



