DOUBT UOL SPECIES. 41 



DOUBTFUL SPECIES. 



The forms which possess in some considerable degree 

 the character of species, but which are so closely similar 

 to other forms, or are so closely linked to them by interme- 

 diate gradations, that naturalists do not like to rank them 

 as distinct species, are in several respects the most impor- 

 tant for us. We have every reason to believe that many of 

 these doubtful and closely allied forms have permanently 

 retained their characters for a long time ; for as long, as far 

 as we know, as have good and true species. Practically, 

 when a naturalist can unite by means of intermediate links 

 any two forms, he 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 enu- 

 merate, 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 com- 

 monly 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 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 competent judges. 



That varieties of this doubtful nature are far from uncom- 

 mon, 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 num- 

 ber of forms have been ranked by one botanist as good 

 species, and by another as mere varieties. Mr. H. C. Wat- 

 son, to whom I lie under deep obligation for assistance of all 

 kinds, has marked for me 182 British plants, which are gen- 

 erally considered as varieties, but which have all been ranked 



