E. V. Wulff — 206 — Historical Plant Geography 



In our opinion neither viewpoint is correct. Geographical elements 

 undoubtedly are fundamental for an understanding of a flora, and an 

 analysis of a flora should begin with these elements. But if we restrict 

 ourselves and do not go more deeply into the genetic significance of 

 these geographical elements, we cannot arrive at any conclusions as to 

 the history of development of a flora. At the same time, the classi- 

 fication of elements solely on the basis of their significance for the 

 genesis of a flora is entirely impossible without a preliminary grouping 

 of species according to their geographical distribution. Hence, it is 

 clear that in analyzing a flora we should not restrict ourselves to either 

 type of elements but should simultaneously study both. 



Moreover, the grouping together of species that entered into the 

 composition of a given flora by a common route and the grouping to- 

 gether of species that were enabled to spread during the same historical 

 period are likewise of prime importance for an understanding of the 

 historical development of floras. It is equally of importance to know 

 which species may be grouped together because of like ecological 

 peculiarities that contributed to their entering into the composition of 

 the given flora. 



In other words, an analysis of a flora, made with the aim of estab- 

 lishing its origin and the history of its development, achieves its pur- 

 pose only in case it is carried out on the basis of the subdivision of the 

 flora into all possible types of elements. Only by such an analysis, 

 culminating in a thorough, comparative study of all the accumulated 

 data, is it possible to understand a flora, to understand, so to say, its 

 philosophy. 



Let us now briefly survey the difficulties involved in referring a 

 species belonging to a flora under analysis to one or another type of 

 element. Thus, as regards geographical elements, it is not possible in 

 all cases to establish the full extent of the area of a species without 

 preliminary study. In many cases a monographic study of a species 

 is necessary in order to define its area precisely. But even in the case 

 of those species whose areas have been established, it is by no means a 

 simple matter to refer them to one or another geographical group. This 

 is clear from the fact that investigators often disagree as regards the 

 geographical distribution of one and the same species. Thus, out of a 

 long list of such disagreements cited by Wangerin we may take as an 

 example Dianthus superbus. Oltmanns referred it to Atlantic species, 

 i.e., to plants of a humid climate; Gradmann included it in a group of 

 continental forest plants; Hummel considered it to be a Euro-Siberian 

 species; Hegi — Eurasian; Steffen — Sarmatian-Central European. 

 The possibiUty of such diversity of opinion arouses doubts as to the 

 significance of analyses of floras divided into groups on such a basis._ 



A correct decision as to the geographical element to which a species 

 should be referred may be made only by locating the mass center of the 

 area of the species, for by this means we can determine which part of 

 this particular area is basic. It is quite apparent, however, that this 

 does not make the task easier but rather comphcates it. Nevertheless, 

 it is in this direction that studies of areas should proceed, since only in 

 this way will there be excluded any danger of subjectivity in the evalu- 

 ation of an area and will there be created the possibility of an objective 



