ASSOCIATION 



The principle of association is the fundamental law of 

 vegetation. Indeed, association is vegetation, for the indi- 

 vidual passes into vegetation, strictly speaking, at the 

 moment when other individuals of the same kind or of 

 different kinds become grouped with it. It is then (and the 

 same statement necessarily holds for vegetation) the coming 

 together and the staying together of individuals and, ulti- 

 mately, of species. A concrete instance will illustrate this 

 fact. In the development of the blowout formation of the 

 Nebraska sandhills (Bedfleldia-Muhlenbergia-anemodium), as- 

 sociation begins only when the first plant of BedHeldia Hex- 

 iiosa is joined by other plants that have sprung from it, or 

 have wandered in over the margin of the blowout. Hence- 

 forth, however dynamic the blowout may remain, or how- 

 ever static it may become, association is a settled character- 

 istic of it until some new and overwhelming physical cat- 

 astrophe shall destroy the associated individuals. It will 

 readily be seen that association does not depend upon par- 

 ticular individuals, for these pass and others take their 

 place, but that it does depend essentially upon number of 

 individuals. 



Association involves the idea of the relation of 

 plants to the soil, as well as that of plants to each other. 

 It is synonymous with vegetation only when the two re- 

 lations are represented, since there may be association such 

 as that of a parasite with its host, which does not constitute 

 vegetation. But it will be seen that the relation of the para- 

 site to the host is practically identical with the relation of 

 the plant to the soil or stratum, and the two concepts men- 

 tioned above become merged. Prom this it follows that 

 association results in vegetation only when the two ideas 

 are distinct. The concept of association contains a fact that 

 is everywhere significant of vegetation, namely, the likeness 

 or unlikeness of the individuals which are associated. In 

 the case of parasite and host, this unlikeness is marked ; in 

 vegetation, all degrees of similarity obtain. As will be evi- 

 dent when the causes which lead to association are con- 



