INTRODUCTION. 15 



gave fairly uniform and thoroughly usable results in the hands of many workers for more 

 than a century and a half. Even though supported chiefly by tradition, it has provided 

 a stable basis for species that was quickly lost when segregation became the usual prac- 

 tice. However, preliminary statistical and experimental studies indicate that the 

 traditional concept was in essential agreement with the evolution of specific stocks, while 

 the concept used in segregation yielded only minor and recent modifications of this 

 stock. With respect to convenience and usability, the traditional concept has everything 

 in its favor, in that it builds upon existing knowledge, permits the recognition of few 

 new species in well-known floras, assigns definite limits characterized as a rule by actual 

 gaps in evolution, and affords the opportunity to relate minor variations to the major 

 stock. As already indicated, the concept applied in segregation enormously increases 

 the number of species, overwhelms specific stocks in a flood of segregates of all possible 

 values, and thus destroys or obscures the main body of taxonomic knowledge. Conse- 

 quently, if taxonomy is to be either stable or usable, it must still rest upon the species 

 concept of Linnaeus and the practice of eminent taxonomists from his time to the present. 

 No change of concept can be made on scientific grounds until the species so founded 

 have been tested by statistics and experiment, and the evidence at present available 

 indicates that these methods will confirm rather than modify the traditional and the 

 evolutionary view of the species (cf. Clausen, 1922). 



The thesis that species can be recognized only in the field would seem to require no 

 argument, were it not for the fact that they are seldom made there. It is probable that 

 few taxonomists would take exception to this statement, but many would question the 

 practicability of the field method, and would incline to regard occasional collecting trips 

 as a fair substitute. Moreover, custom itself furnishes a strong argument in favor of 

 the herbarium as the place for recognizing species. These have always been "made" in 

 the herbarium; why not continue to make them there? Reasons of convenience tell 

 most strongly in favor of continuing this practice. The field is often distant, and the 

 expense of field work heavy if not prohibitive. The field is available for work but a 

 small part of the year in many regions, and personal convenience, as well as such duties 

 as teaching, is often a deciding factor. Moreover, one works much faster by the her- 

 barium method, and results accumulate much more rapidly. An even more cogent 

 reason is the fact that types are available only in herbaria, and it is natural to feel that 

 critical work can be done only in contact with them. However, the most compelling 

 reason is that of tradition and custom, combined with the fact that no field method has 

 heretofore been developed for the study of species. With this available, it is confidently 

 to be expected that taxonomy, like other scientific subjects, will turn to the field as the 

 one place in which material and process are fully available, and in which results will 

 meet the most critical requirements as to scientific quality and permanence. 



From the above, it follows that evolutionary taxonomy must regard the segregates 

 of the last 25 years chiefly in the light of tentative proposals as to the course of evolution. 

 It is imperative to reestablish species on the basis of the traditional concept as exemplified 

 in America by Gray and those that have worked in a similar manner since. The fact 

 is not ignored that all the master taxonomists recognized some forms that were not species 

 according to their own concept (Chase, 1921), but this was exceptional and had no appre- 

 ciable efifect on the body of their species. The application of statistics and experiment 

 to certain species of the "Synoptical Flora" has shown that a relatively small number 

 are to be treated as variads. It is significant of Gray's concept and the basis of relation- 

 ship behind it that in nearly every doubtful case he pointed out the inadequacy of the 

 form as a species. These are the first of which the vaUdity requires statistical test, in 

 order that a coherent and uniform body of species that meet the evloutionary demands 

 may be established. Even before this is completed, however, it is possible and desirable 



