VARIATION AND DISTRIBUTION OF SPECIES. 135 



Such being the results of the want of adequate knowledge, 

 how is it likely to be when our knowledge is largely in- 

 creased? The judgment of so practised a botanist as De Can- 

 dolle is important in this regard, and it accords with that of 

 other botanists of equal experience. 



" They are mistaken," he pointedly asserts, " who repeat 

 that the greater part of our species are clearly limited, and 

 that the doubtful species are in a feeble minority. This 

 seemed to be true, so long as a genus was imperfectly known, 

 and its species were founded upon few specimens, that is to 

 say, were provisional. Just as we come to know them better, 

 intermediate forms flow in, and doubts as to specific limits 

 augment." 



De Candolle insists, indeed, in this connection, that the 

 higher the rank of the groups, the more definite their limita- 

 tion, or, in other terms, the fewer the ambiguous or doubtful 

 forms ; that genera are more strictly limited than species, 

 tribes than genera, orders than tribes, etc. We are not con- 

 vinced of this. Often where it has appeared to be so, advanc- 

 ing discovery has brought intermediate forms to light, per- 

 plexing to the systematist. " They are mistaken," we think 

 more than one systematic botanist will say, " who repeat 

 that the greater part of our natural orders and tribes are 

 absolutely limited," however we may agree that we will limit 

 them. Provisional genera we suppose are proportionally 

 hardly less common than provisional species ; and hundreds of 

 genera are kept up on considerations of general propriety or 

 general convenience, although well known to shade off into 

 adjacent ones by complete gradations. Somewhat of this 

 greater fixity of higher groups, therefore, is rather apparent 

 than real. On the other hand, that varieties should be less 

 definite than species, follows from the very terms employed. 

 They are ranked as varieties, rather than species, just because 

 of their less definiteness. 



Singular as it may appear, we have heard it denied that 

 spontaneous varieties occur. De Candolle makes the impor- 

 tant announcement that, in the Oak genus, the best known 

 species are just those which present the greatest number of 



