Variation, Geographical Distribution, and Succession, S5 



were founded upon few specimens — that is to say^ were pro- 

 visional. Just as we come to know them better, intermediate 

 forms flow in, and doubts as to specific limits augment." 



DeCandolle insists, indeed, in this connexion, that the higher 

 the rank of the groups, the more definite their limitation, 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, &c. We are not convinced of this. Often, 

 where it has appeared to be so, advancing discovery has brought 

 intermediate forms to light, per2:)lexing to the systematist. 

 " They are mistaken," we think more than one systematic bota- 

 nist 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 spon- 

 taneous varieties occur. DeCandolle makes the important an- 

 nouncement that, in the Oak genus, the best-known species are 

 just those which present the greatest number of spontaneous 

 varieties and subvarieties. The maximum is found in Q. robur, 

 with twenty-eight varieties, all spontaneous. Of Q. Lusitanica 

 eleven varieties are enumerated, of Q. Calliprinos ten, of Q. cocci- 

 fera eight, &c. And he significantly adds that "these very 

 species which offer such numerous modifications are themselves 

 ordinarily surrounded by other forms provisionally called spe- 

 cies because of the absence of known transitions, or variations, 

 but to which some of these will probably have to be joined here- 

 after." The inference is natural, if not inevitable, that the dif- 

 ference between such species and such varieties is only one of 

 degree, either as to amount of divergence or of hereditary fixity, 

 or as to the frequency or rarity, at the present time, of inter- 

 mediate forms. 



This brings us to the second section of DeCandolle's article, 

 in which he passes on, from the observation of the present 

 forms and affinities of Cupuliferous plants, to the consideration 

 of their probable history and origin. Suffice it to say that he 

 frankly accepts the inferences derived from the whole course of 

 observation, and even contemplates with satisfaction a probable 



