6 THE PHYLOGENETIC METHOD IN TAXONOMY. 



territory and growing in a considerable range of differences within the habitat, or often 

 in different habitats. An analysis based upon a few herbarium specimens or frequently 

 indeed upon a single one can rarely be more than a personal opinion and usually affords 

 but an erroneous or imperfect impression of the actual species. With reference to the 

 evidence provided by Nature, then, the synthesis of data from various regions is imper- 

 ative if a complete and exact picture of the species is to be obtained. The statistical 

 method itself, while it is analytic in that it deals with individuals, is synthetic in as 

 much as it relates the individuals studied to the mode for the locality as well as for the 

 species. The experimental method appears to be intrinsically analytic, since it deals 

 with the differentiation of the stock. However, its most successful use so far in the 

 field has been to relate ecads to the parent stock and the so-called reciprocals to each 

 other (Clements and Hall, 1922). Moreover, in working with the differentiation of a 

 stock in various habitats, the synthetic factor is given full value at the outset, and the 

 task is then merely one of analyzing the evolutionary possibilities of the species. Finally, 

 the examination of any group of individuals produced experimentally involves the deter- 

 mination of the mode of the departure as well as the extremes. Thus, in building a 

 natural system, synthesis and analysis must go hand in hand; it is the task of analysis 

 to find new facts and of synthesis to give them their proper meaning. 



THE GENUS CONCEPT. 



Nature of the genus. — In the prevalent view the genus appears to be regarded merely 

 as a concept, and it is often stated that it does not actually exist in nature. This is 

 doubtless true for those who regard the genus merely as a pigeon-hole, chiefly convenient 

 for the filing of new species. Such a view has its justification in the usual practice 

 of making genera, and especially in the recent flood of generic segregation. It is not 

 supported by the evidence drawn from the methods of evolution or the record of phy- 

 logeny. To the student of evolution, the genus represents a certain characteristic portion 

 of the line or field of specialization, and its existence is as definite as that of the species 

 which constitute it. It may be more difficult to recognize, but this is primarily the 

 fault of outlook and method. In the absence of definite criteria, the chief difficulty 

 centers about the rank and limits of genera. As a consequence of the unrestricted 

 play of personal opinion, not infrequently aided by bias or carelessness, present-day 

 taxonomy contains genera of every possible quality. Many of these disappear com- 

 pletely when the test of evolution is applied to them. Given the family, genus, and 

 species as major units, these will regularly be differentiated into tribes, sections, and 

 variads, respectively. This is a necessary corollary of the principle that the processes 

 of evolution are constantly and universally at work. The basic laws of conservation 

 of energy and material, division of labor, and increase of parental care lead inevitably 

 to divergence, and hence to the splitting of the generic stock into sections, and of the 

 specific stock into variads. 



The question of generic limits is one of criteria. These have been of the most various 

 kinds and quality, and have led to results of the most diverse value. It seems obvious 

 that personal opinion is the poorest of bases for determining the relative merits of criteria, 

 and that improvement in this respect can be effected only by means of experimental 

 and statistical studies of the generic criteria in use. Until this is done, the segregation 

 of well-established genera can have no standing in evolutionary taxonomy. 



Genus and section. — The relation of the subgenus or section to the genus is a basic 

 and natural one, arising out of evolution and serving as a record of it. It was inevitable 

 that genera of wide extent in contact with many effective habitats, such as circum- 

 polar ones, should show wide differentiation. The generic stock became split up into 

 several or many lines of evolution, each with its secondary development. So funda- 



