340 



SCIENCE 



[N. S. Vol. XLV. No. 1162 



classified by means of serai imits as well as by 

 climax -units. Both methods have been used 

 by various investigators rather indiscrimi- 

 nately, or at least no particular model (if 

 there be such) has been followed consistently. 

 Clements rightly emphasizes the desirability 

 of working out and adopting a set of terms 

 to cover these two concepts of vegetation and 

 he goes so far as to propose terms by means 

 of which the various climax and serai fea- 

 tures of the plant formation may be described. 

 The reviewer is aware of the advantages and 

 disadvantages of the various systems which 

 have been proposed in the past and we must 

 confess that this latest proposal is perhaps 

 still far from the ideal, and yet it represents an 

 advance, it marks progress. At least it serves 

 to focus the attention upon the dynamic phases 

 of vegetation as apart from the static. The 

 author may be criticized for the introduction 

 of new terms in this connection, but new 

 concepts or relations may be expressed only 

 by appropriate words. Scientific men should 

 not be confounded by the introduction of an 

 occasional new term. 



The climax units which Clements proposes 

 are: associations, climax communities which 

 associated regionally constitute the formation ; 

 co7isociationSj the units of the association, 

 characterized by a single dominant species; 

 societies, communities within an association 

 or consociation controlled by one or more sub- 

 dominant species; and clans or aggregations 

 of secondary species within either of the above 

 subdivisions. The clan is quite local and often 

 not sharply delimited from the society. 



Serai units are analogous to climax units 

 or communities throughout the course of suc- 

 cession. These units are proposed in order to 

 point out sharply the distinctions between the 

 developmental or dynamic and climax or 

 static phases of vegetation. The associes is 

 the developmental equivalent of the associa- 

 tion, differing from the latter only in its 

 transient nature. The consocies corresponds 

 to the consociation in the same manner that 

 associes corresponds to association. " The 

 consocies is a serai community marked by the 

 striking or complete dominance of one species, 



belonging, of course, to the life-form typical of 

 that stage of development." The socies is 

 likewise the developmental equivalent of the 

 society. The colony is an initial community 

 of two or more species. Colonies resemble 

 clans in their limited size and absence of 

 clearly defined relation to the habitat. From 

 their appearance in bare areas colonies are 

 nearly always sharply delimited. The inva- 

 sion of weeds frequently follows the colony 

 type of grouping. The family is a group of 

 individuals belonging to one species. Because 

 of this nature families are quite rare in gen- 

 eral, but they are common in bare areas and in 

 the initial stages of a succession. This at- 

 tempt to work out a classification of vegeta- 

 tion types founded upon the developmental 

 basis should appeal to all broad-minded stu- 

 dents of plant ecology. 



Another valuable portion of Clements's book 

 is the part devoted to the climax formations 

 of North America as summarized from the 

 available literature. 



Suceessional studies in Eurasia are also ab- 

 stracted. 



An extended portion of the monograph is 

 devoted to a discussion of " past climates and 

 climaxes " or to the succession of vegetation 

 in remote times as revealed in the geological 

 record. " The operation of succession was 

 essentially the same during the geological past 

 that it is to-day: from the nature of their 

 vegetation forms, the record deals largely with 

 the ultimate stages of such successions. It is 

 evident that geological succession is but a 

 larger expression of the same phenomenon, 

 dealing with infinitely greater periods of time, 

 and produced by physical changes of such 

 intensity as to give each geological period its 

 peculiar stamp. If, however, the geological 

 record were siifficiently complete, we should 

 find unquestionably that these great succes- 

 sions merely represent the stable termini of 

 many series of smaller changes, such as are 

 found everywhere in recent or existing vege- 

 tation. ... In short, the development and 

 structure of past vegetation can be imderstood 

 only in consequence of the investigation of 

 existing vegetation." 



