276 George E. Nichols, 



of any climatic region constitutes a climatic formation. To sum 

 up : the association is a unit determined by habitat ; the edaphic 

 formation is a unit determined by physiography — a unit of a 

 higher order than the association; while the climatic formation 

 similarly is a unit determined by climate — a unit of a still higher 

 rank than either of the preceding. 



In the account of the ecological relations of the vegetation of 

 northern Cape Breton which follows, the two climatic forma- 

 tions here represented are discussed separately. The scheme 

 followed in classifying the innumerable associations which, taken 

 collectively, comprise the vegetation of the respective regions 

 concerned is partially outlined in the table of contents, which 

 may be looked upon as in the nature of an analytical key. For 

 the benefit of readers to whom the writer's paper on classifica- 

 tion may not be available, a few further remarks regarding the 

 system on which this synopsis is built up may be added. 



First of all, taking into account their successful relations to 

 one another and their distribution with reference to specific 

 physiographic unit areas, the various individual units of vegeta- 

 tion, the associations, have been assembled into definite associa- 

 tion-complexes. An individual association-complex, as thus 

 defined, constitutes an edaphic formation. For obvious reasons, 

 however, the various individual associations have been treated 

 collectively, as association-types, and, similarly, emphasis has 

 been laid on the edaphic formation-types rather than on the 

 individual formations (see definitions above). Proceeding fur- 

 ther, the edaphic formations (and formation-types) of the region 

 have been divided primarily with reference to the water rela- 

 tions of the areas which they occupy into two successional 

 series : formations of the xerarch series, and formations of the 

 hydrarch series.'* Under each of these two heads, in the case 

 of the region of deciduous forests, it has seemed desirable to 

 distinguish between primary and secondary formations, the latter 

 embracing formations in which the vegetation has been modified 



^The term xerarch, to quote Cooper ('13, p. 11), "is applied to those 

 successions which, having their origin in xerophytic habitats, such as rock 

 shores, beaches, and cliffs, become more and more mesophytic in their 

 successive stages; . . . [the term hydrarch] to those vi^hich, originating 

 in hydrophytic habitats, such as lakes and ponds, also progress toward 

 mesophytism." 



