SERAL UNITS. 



137 



development is held indefinitely in a subelimax stage, as in heath and prairie. 

 On the other hand, a change of climate which advances the climax converts the 

 previous associations into developmental units, and they thus become associes. 

 This potential relation between association and associes naturally obtains 

 wherever climax associations are zoned. This is especially evident in moun- 

 tain regions, where grassland and scrub associations are potential associes of 

 the forest above (plate 39, a, b). 



In its complete expression, the associes is marked by striking changes of both 

 habitat and life-form, as necessarily of floristic. This is best illustrated in 

 water seres, the initial stages of which constitute three well-marked associes, 

 namely, submerged plants, floating plants, and swamp plants. In each there 

 is a pronounced change of habitat necessarily accompanied by a corresponding 

 change of life-form and floristic. While it seems probable that all important 

 changes of life-folm are due to the reaction upon the habitat, certainty in 

 this respect is impossible as yet. It can be attained only by the instrumental 

 study of conditions before and after the change of life-form. Theoretically, 

 such a relation seems highly probable, and we may assume as a working 

 hypothesis that one associes is limited from another by important changes of 

 habitat, as well as life-form. In the prisere of the spruce-fir formation 

 (p. 74), for example, it is probable that the change from crustose to foliose 

 lichens is as great a change of habitat as happens anywhere in the sere, but it 

 is too minute in extent to be impressive. 



While associes is obviously from the same root as association, it is based 

 upon the original meaning of sequence {sec-, soc-, follow) rather than the 

 derived one of companionship. Though the form assedes is preferable for 

 some reasons, it is less euphonic and less suggestive of the relation of associa- 

 tion. It seems desirable to emphasize the relationship between the two units 

 by terms evidently related rather than to employ a wholly new word. For 

 the same reason the names of particular associes are based upon the words 

 already used for formation and association. These three units have so much 

 in common that the same root modified by a different suflBx seems to harmonize 

 readily with the actual degree of similarity and difference. For associes, the 

 termination -is is proposed, and we would thus have helis, pais, hylis, eremis, 

 etc., e. g., Sdrpus-Typha-helis, Andropogrni-Aristida-pms, etc. 



Consocies. — The consocies is a serai conmiunity marked by the striking or 

 complete dominance of one species, belonging of course to the life-form 

 typical of that stage of development (plate 40, a, b) . It is the unit of the asso- 

 cies in the same way that the consociation is of the association. The con- 

 socies and consociation differ only in that the former is a developmental or 

 seraJ, the latter a climax, community. Bouteloua and BvMKs are consocia- 

 tions of a climax association of the Great Plams, Andropogon scoparius and 

 Anstida purpurea are consocies of a serai association, or associes. Because 

 of its developmental nature, the reed-swamp association is an associes in the 

 present conception, and each of its dominants, Sdrpus, Typha Phraomites 

 etc., forms a consocies. The heath association is likewise an associes excent 

 where It may have been stabOized to form a climax, and CaUuna and Erica 

 form the characteristic consocies of it. 



The term consocies likewise is obviously related to consociation. In the 

 latter, however, the sufiix emphasizes the condition of being grouped together. 



