44 JOURNAL OF THE ARNOLD ARBORETUM [vol. i 



NEW SrECIES, VARIETIES AND COMBINATIONS FROM THE 



HERBARIUM AND THE COLLECTIONS OF THE 



ARNOLD ARBORETUM 



Alfred Rehder 



The purpose of this paper Is to i)ublish a number of new combinations, new 

 species, new varieties and forms, as well as to record various observations 

 which have presented themse]\es in the course of a systematic rearrange- 

 ment of the herbarium of the Arnold Arboretum and while working on a 

 manual of cultivated trees and shrubs. Particularly the a])i)lication of the 

 International Rules of nomenclature to the material preserved In our her- 

 barium has made new combinations necessary, and a few words therefore 

 may be said of the principles guiding these nomenclatorlal changes. 



The interpretation of certain articles of the International Rules has been 

 always subject to a diversity of opinion, due chiefly to more or less vague- 

 ness In the wording of these articles and to the introduction into the rules 

 of the ly[yG method, to which nearly all American botanists now adhere and 

 which ai)parently is gaining more and more foothold abroad, as shoA\Ti by 

 the additional recommendaticm, xviiibis, In the revised code which reads: 

 *' When publishing names of new groups to indicate carefully the subdivi- 

 sion which is regarded as the t;^l>c of the grou]): the typical genus in a fam- 

 ily, the typical species in a genus, the typical variety or specimen in a 

 species." One of the most im])ortant consequences of the acce])lance of 

 the type method is a different attitude in regard to articles 45 and 47 dealing 

 with the division of groups. 



It is not the j>lace here to enter into a discussion as to how to determine 

 the type of genera and si)ecies and it is, moreover, hardly possible to formu- 

 late general rules for the determination of ty]^cs, as each case must be con- 

 sidered and judged on its OAvn merits, but it may safely be stated that the 

 number of cases where one cannot reach a conclusive decision is compara- 

 tively small. The difTiculty lies chiefly with those who consider a group to 

 be a conception, that is, a genus a group of s]>ecies, and a s])ecies a group of 

 individuals or minor forms joined together by common characters and cir- 

 cumscribed by a description, instead of taking the position that the groups 

 or individuals are assembled around a group or an individual whi(*h is con- 

 sidered the typical re])rcscntative; however much or however little a group 

 is changed by additions or sul)tractions, it always keei>s the same name wilh 

 the citation of its original author as long as it contains the typical form. 

 Those who view a group as a conception are easily led to abandon a specific 



name on the plea that it is composed of different elements, if it contains 

 forms which according to our ]>resent point of view re]>resent different 

 si>ecles, or in the case of a genus to resort to counting the number of 

 sj)ecies and leaving the name with the largest number. There is, no doubt, 

 great difficulty in determining the generic ty]>e in some of the old Linnaean 

 genera like Sorbus, Crataegus, Prunus, and for such cases the doctrine of 



