RECENT INVESTIGATIONS. 29 



Clements, 1902-1904. — In "Herbaria Formationum Coloradensium" (1902) 

 and its continuation, "Cryptogamae Formationum Coloradensium" (1906- 

 1908), Clements endeavored to organize an herbarium method of indicating 

 and recording the structure and development of vegetation. This method 

 was discussed briefly in "Formation and Succession Herbaria" (1904), and 

 the analysis of the Colorado vegetatipn proposed in the collections mentioned 

 was sketched in its main details. The formations recognized were largely 

 climax associations of the mountain clisere, and were arranged in the corre- 

 sponding sequence. Many of them, however, were the developmental asso- 

 ciations, now distinguished as associes, and these were grouped in the serai 

 sequence. The structure of each was indicated by the grouping of the species 

 into facies, aspects, principal and secondary species, marking consocies, socies, 

 clans, and colonies respectively. 



Clements, 1904- — In the "Development and Structure of Vegetation," 

 Clements made the first attempt to organize the whole field of present-day 

 succession, and to connect the structure of vegetation with its development in 

 the essential way that these are related in the individual plant. The concept 

 was advanced that vegetation is an entity, whose changes and structures are 

 in accord with certain basic principles in much the same fashion that the func- 

 tions and structures of plants follow definite laws. The treatment falls into 

 five divisions, association, invasion, succession, zonation, and alternation. Of 

 these, invasion and succession are developmental processes, and association, 

 zonation, and alternation the basic expressions of structure which result from 

 them. Invasion was defined as the movement of plants from one area to 

 another, and their colonization in the latter. Invasion was analyzed into 

 migration, or actual movement into a new place, and ecesis, the estabhshment 

 in the new home. Migration was considered with reference to mobility, 

 organs modified for dissemination, migration device, agents, and direction. 

 Barriers, endemism, and polygenesis were discussed in connection with ecesis, 

 while invasion was further considered with reference to kinds and manner. 

 The necessity of using quadrats and migration circles for the exact study of 

 invasion was also emphasized. 



After a historical sunamary of the development of the idea of succession, the 

 latter was related to invasion, and successions were classified as normal, 

 divided into primary and secondary, and anomalous. Primary and secondary 

 successions were grouped upon the basis of agent or process, e. g., elevation, 

 volcanic action, weathering (residuary soils), gravity (colluvial soils), water 

 (alluvial soils), etc.*(c/. Chapter IX). The reactions of serai stages were next 

 analyzed in detail, and the laws of succession were grouped under the follow- 

 ing heads: (1) causation, (2) reaction, (3) proximity and mobility, (4) ecesis, 

 (5) stabihzation, (6) general laws. The treatment was concluded by a dis- 

 cussion of classification and nomenclature and of methods of investigation. 



Friih and Schroter, 1904. — ^Although they did not deal specifically with suc- 

 cession, the monumental monograph of Friih and Schroter upon the Swiss 

 moors is a mine of successional material of the first importance. As the 

 botanical portions are sununarized in a later chapter, it will suffice here to 

 indicate the scope and nature of the work by giving its main heads. 



