592 PLANT GROWTH AND PLANT COMMUNITIES 



criteria (mostly genetic) have gained much ground over descriptive 

 ones. 



If such a trend is to be followed in placing the plant communities 

 of a region in some kind of relative order, then their genetic features 

 should be of the utmost significance. But what can be properly con- 

 sidered a genetic feature in a plant community? Is it too tenuous an 

 analogy to make the following equation? 



species-population gene 



community species 



One might not be prepared to go so far as to add: 



species species-population 



association community 



The considerations offered above concerning the anatomy and the 

 physiology of the plant community, if applied with a certain rigor and 

 uniformity, will indeed characterize them individually so well that they 

 can be readily distinguished from one another. It is only another step 

 to attempt to lump together all the communities that are located in the 

 same range of variation for each of these criteria. I have made an ex- 

 periment in this direction. In 1946 I had designed a pattern of 30 plant 

 communities in the Montreal area which showed their points of con- 

 tact and their probable mutual (successional) relationships. This pat- 

 tern of associations can now be analyzed by superimposing upon it any 

 of the criteria deemed significant. Thus I have recently ( 1960 ) drawn 

 upon the same pattern the distribution of layering and coverage, of 

 periodicity, of ecosystematic control, and of successional status, all of 

 which follow non-coincident lines. For instance, evergreenness im- 

 pinges upon forest and scrub formation types, upon consolidation, 

 subclimax, and quasiclimax stages, etc. 



This would tend to show that synecological units can be regrouped 

 in a number of ways— in as many ways as there are criteria. Table XI 

 gives a tentative alignment of values of each of the criteria that have 

 been considered in the sections above. It is suggested that a community 

 which has attained a high degree of sociological differentiation and is 

 the climax of a regional complex generally has the qualities listed on 

 the right. Its floristic composition reveals a great richness, some uni- 

 formity of geographical range, a degree of ecological specialization, 

 and few species "out of place." Its structure shows dense coverage, 

 with a somewhat complex layering, consisting of a fair representation 

 of many life forms and leaf types. Physiologically, its periodicity is 



