120 STRUCTURE AND UNITS OF VEGETATION. 



smaller units, which is by no means unfortunate, since it indicates nothing else 

 than greater accuracy. As a consequence, floristic studies are always a sub- 

 stitute for pure physiognomic or ecological viewpoints, but the converse is 

 not true. Moreover, the floristic method has the advantage of being purely ana- 

 lytical and hence highly objective. It is independent of physiological theories 

 and does not presuppose a knowledge of causal relations, but leads up to it. 

 It permits one to reckon with habitat and adaptations, as well as with unknown 

 factors; it proposes problems, and it stimulates to new investigations and 

 advances. Through refining this method of determining the controlling 

 factors by means of floristic agreements and contrasts, one can certainly obtain 

 much insight into the factors of plant life, which have heretofore been over- 

 looked. Thus, while the floristic analysis stands out as the most exact, most 

 objective and most fruitful, and indeed as the sole universally applicable 

 expression of the formational facts, yet it in no wise excludes the consideration 

 of other viewpoints, but on the contrary encourages their use. Nothing stands 

 in the way of adding to the floristic characterization a thorough analysis and 

 description of the environic, physiognomic, ecologic, phytogeographic, and 

 developmental relations. The chief emphasis must fall upon these funda- 

 mental investigations and for these the floristic has only to furnish a basis 

 free from objections. But such viewpoints can not serve for the limitation of 

 formations; moreover, there is nothing to be gained from dubious and arbi- 

 trary compromise. I hold therefore that we must universally recognize the 

 floristic composition not merely as an important, but much rather as the basic 

 and decisive criterion for the recognition of plant formations." 



Warming's concept. — ^Warming (1895) assigned to the habitat the chief 

 value in determining plant commimities. As he rejected the term "forma- 

 tion," however, it is impossible to obtain his concept of the formation at this 

 time. In the second edition of his pioneer work (1909 : 140), he expresses the 

 concept as follows: 



"A formation may then be defined as a community of species, all belonging 

 to definite growth forms, which have become associated together by definite 

 external (edaphic or climatic) characters of the habitat to which they are 

 adapted. Consequently, as long as the external conditions remain the same, 

 or nearly so, a formation appears with a certain determined uniformity and 

 physiognomy, even in different parts of the world, and even when the con- 

 stituent species are very different and possibly belong to different genera and 

 families. Therefore — 



"A formation is an expression of certain defined conditions of life, and is not 

 concerned with floristic differences. 



"The majority of growth forms can by themselves compose formations or 

 can occur as dominant members in a formation. Hence, in subdividing the 

 groups of hydrophilous, xerophilous, and mesophilous plants, it will be natural 

 to employ the chief types of growth forms as the prime basis of classification, or, 

 in other words, to depend upon the distinctions between trees, shrubs, dwarf- 

 shrubs, undershrubs, herbs, mosses and the Uke." 



Moss (1910 : 39) has criticized Warming's concept of the formation, which 

 treats the latter as a subjective group comprising all associations of like 

 physiognomy. He considers that: 



"Warming has given the concept an unfortunate bias, and that his view is 

 sufficiently at variance with historical and present-day usage to demand some 

 examination of his treatment of this unit of vegetation. Confusion is apparent 



