14 ASSOCIATION 



(J855) ignores formations and treats only incidentally of 

 stations : this is explained by the fact that he wrote of 

 botanical geography, considering the treatment of stations 

 to belong to botanical topography. With the work of 

 Kemer (J863),Gtisebach (1872), Engler (1879), Hult (I88I,J885), 

 Goeze (1882), Beck (J884), Drude (1889) and Warming (t889), 

 the recognition and delimitation of formations came to con- 

 stitute the foundation of vegetational research, a relation 

 •which the work of the last decade has greaily emphasized. 

 At the present time, the formation stands in precisely the 

 same relation to vegetation, and hence to phytogeography, 

 that the species does to the flora, and to taxonomy. In con- 

 sequence, the primary lines of research are the same for 

 each, and the foundations of phytogeography must be laid 

 upon the development, structure and classification of for- 

 mations in the same thorough way that the superstructure 

 of taxonomy has been built upon the development, structure 

 and classification of species. 



Since the present paper deals with vegetation as a whole, 

 the development of formations will be treated under succes- 

 sion, the structure of formations under zonation and alter- 

 nation, while their classification will be found under associ- 

 ation and succession. 



In endeavoring to analyse the causes of association, it 

 must be kept clearly in mind that the concrete examples 

 from which all generalisations must be drawn are often m 

 very different stages of development, and are of correspond- 

 ingly different ages. For this reason, it has seemed best 

 to consider the primary relations of association in general in 

 this place, leaving the treatment of the effects of invasion, 

 succession, alternation, and zonation to be taken up under 

 these topics. 



Various categories of association may be distinguished 

 according to the dominant physical factor concerned, or the 

 point of view taken. These will fall into two series, as we 

 consider the relation of plant to plant with reference to some 

 object or characteristic, or the grouping of plants together 

 in response to some dominant factor. In the first series 



