Chapter I —7— Scope and Method 



paleobotanical data, despite the casual and fragmentary nature of the 

 latter. The importance of such data should not be underestimated, 

 since they constitute the only direct evidence available for establishing 

 the history of a flora. 



By the phylogenetic method we gain a knowledge of the species 

 composing a given flora and of their areas. Deeper investigations along 

 this line lead to monographic studies of certain groups of species most 

 characteristic of selected genera. On the basis of such studies the 

 phylogenetic direction of development of these genera is established, 

 which, combined with data from a study of geographical distribution, 

 points to their centers of origin and to the history of their dispersal 

 from these centers. Combining the results obtained from such a study 

 of genera representing the various floristic groups, we may draw con- 

 clusions as to the trend of development of the entire flora under in- 

 vestigation. 



The establishment of phylogenetic links and relationships between 

 the species composing a given genus is achieved by all possible scien- 

 tific methods, of which the chief is the morphological method. The 

 sequence of changes involving increased complexity of structure of 

 species (morphological, cytological, anatomical, biochemical, etc.) may 

 coincide with changes in the geographical location of individual species 

 or whole sections of a genus. 



The trend of evolution of a genus from primitive representatives to 

 those of more complex structure, from relic forms showing but slight 

 variation to progressive forms, as reflected in their geographical dis- 

 tribution, gives indications as to the probable initial center of develop- 

 ment of a genus, its subsequent geographical migration and the routes 

 of the latter, the formation of secondary centers of diversity, the 

 appearance during the course of such migration of vicarious species, 

 etc. Such a taxonomic study of the genera composing a given flora 

 constitutes a firm foundation for a simultaneous or subsequent study 

 by the botanico-geographical method. If the geographical method has 

 proved to be exceptionally valuable in a taxonomic study of plants, the 

 taxonomic method is, conversely, of no less importance in a historico- 

 geographical study of floras. In every modern botanical monograph 

 may be found numerous examples illustrating the possibility of such 

 use of taxonomic data as an aid to historical plant geography. We 

 shall cite only a few instances of the founding of historico-geographical 

 conclusions on the basis of a phylogenetic study. 



One such case is that of the establishment of the chief features of 

 the history of development of the flora of Mongolia and China by 

 V. L. KoMAROV (1908) on the basis of a study of five genera chosen on 

 account of the nature of their geographical distribution. A mono- 

 graphic study of these genera made it possible to determine the centers 

 of their origin and the routes of their subsequent migration, which, 

 taken together, indicated the trend of development of the entire flora 

 of Mongolia and China. As a second example we may take the phylo- 

 genetic study of the genera of the family Sapotaceae made by Lam 

 (1935), who found that there is a decrease in the number of sepals in 

 the flowers of the more highly organized species and also that there are 

 changes in a number of other morphological characters specific for the 



