INTRODUCTION. 7 



mental and uniform was this process that its consequences are to be found in practically 

 all genera that have attained considerable differentiation of species. It corresponds 

 to the basic law of adaptation and specialization under the pressure of new conditions, 

 and the maintenance of their evolutionary relationship is the chief task in the groups 

 thus produced. The differentiation of the sections is subsequent and subordinate to 

 that of the genus, and any treatment that ignores or obscures this fact is as undesirable 

 as it is unnatural. To all who recognize that taxonomy should be the best possible 

 interpretation of evolution, the confusion of genera and subgenera appears to negative 

 all the principles upon which evolutionary taxonomy should rest. 



Generic segregation. — The general tendency, during the last two decades in America 

 at least, has been to segregate genera by raising their sections to generic rank. While 

 the practice is not confined to this period, it is characteristic of it. Not all large genera 

 have received this treatment as yet, but another decade or two will see this done, unless 

 it is given a sharp check by the scientists who suffer from it. This tendency to assign 

 generic rank to smaller and smaller divisions is the natural result of studies by specialists, 

 who often focus their attention upon details to an extent that magnifies them out of 

 all proportion to their value. Relationship and perspective are lost, and the results 

 are both unnatural and unusable. It is necessarily in the largest and best-known 

 genera that segregation has been rife, and it is these that offer the greatest opportunity 

 for damage, both to phylogeny and to classification. In North America, Astragalus 

 is unique in that it is now represented by 19 genera, socalled; Aster is segregated into 13, 

 Haplopappus into 11, and Gilia, Oenothera, and Saxifraga are broken up into 10 or 

 more each. Habenaria and Polygonum are each split into 6 parts, Claytonia, Euphorbia, 

 Lotus, and Ranunculus into 5, and a large number of genera into 4 and 3. 



While no complete presentation of the arguments for segregation seems to be available, 

 the major reasons may be gained from various sources. It is contended that many 

 genera, including those mentioned above, are unnatural groups of species of diverse 

 habit and structure, and that they should be split into smaller and more natural ones. 

 A second argument is that genera should be uniform, and that the criteria used in certain 

 groups should be applied throughout. This is akin to the contention that many small 

 genera are more convenient than a few large ones, and that a genus should be auto- 

 matically split up when the species reach a certain number. Finally, it is sometimes 

 maintained that justice to obscure workers demands that their genera should be adopted, 

 since they are as good as many of those already in use. 



Failures of segregation. — The most conspicuous failure of the method of generic 

 segregation is in connection with phylogeny and classification. The 18 segregates of 

 Astragalus are much more nearly related to each other than they are to Robinia or 

 Trifolium, but there is no evidence of this fact in their treatment. The only possible 

 phylogenetic and taxonomic treatment of these is to include them in Astragalus as 

 sections, differentiated more or less recently from the same generic stock. This is like- 

 wise the answer to the contention that Astragalus, Aster, Gilia, Gentiana, Oenothera, etc., 

 are unnatural groups, and that they are rendered more natural by raising their sections 

 to generic rank. If further answer is sought, it may be obtained by trying to locate 

 an Astragalus in the 18 segregates that represent its sections. The endeavor to give 

 criteria the same value throughout and to make genera uniform fails because evolution 

 is far from uniform, and its products share this quality. Moreover, it is significant 

 that practically all such attempts confine themselves to reducing genera to the rank 

 of the least valid, instead of combining the less natural genera to increase their validity 

 in terms of evolution and relationship. 



The assumption that many small genera are more convenient than fewer large ones 

 shows a curious ignorance of the significance of system, and of the mechanism of memory. 



