Chap. H.] DOUBTFUL SPBCIBS. 



57 



unite by means of intermediate links any two forms, 

 ne 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, some- 

 times arise in deciding whether or not to rank one form 

 as a variety of another, even when they are closely con- 

 nected 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 natural- 

 ists having sound judgment and wide experience 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 com- 

 petent 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 varie- 

 ties. Mr. H. C. Watson, to whom I lie under deep 

 obligation for assistance of all kinds, has marked for 

 me 183 British plants, which are generally considered 



