BOOKS AND CURRENT LITERATURE 51 



More thorough study will undoubtedly enable future investigators 

 to improve greatly the system here proposed. Still the application of 

 this system, with a constant desire to test the conclusions which it 

 forces, and not a slavish adherence to the plan will undoubtedly do 

 much to clear up our present uncertain attitude toward the structure 

 and development of thte plant cover. 



After a brief review the following terms are proposed for the suc- 

 cessional series: A sere is a unit of succession leading to a plant forma- 

 tion. Where this process has been repeated several times on the same 

 area the group is known as a cosere. (The cosere corresponds roughly 

 with the English use of the term formation.) Chsere — a development 

 leading to an adjustment with the cUmate. Eosere — the development 

 during each geological era. Geosere is the development from the first 

 creation of life on the earth to the present time and made up of the 

 eoseres named to correspond to geological eras. A further division 

 into pricere, a primary development; subsere, a secondary development; 

 the hydrosere, a series originating in a water stage; and xerosere, origi- 

 nating in an arid habitat. The hydrosere is divided into the halosere, 

 originating in salt water; and the oxysere, originating in water deficient 

 in oxygen. The xerosere is divided into the lithosere, originating on 

 rock; and the pasammosere, originating on sand. In this chapter is 

 given the author's idea of the climaxes of the different seres or the 

 plant formations. These climaxes are supposed to conform to climatic 

 units. 



The climax formations of North America are discussed and ab- 

 stracts given of studies of successions which have been made within 

 the various formation as well as those in Eurasia and other parts of the 

 world. It becomes evident by a perusal of this chapter that up to the 

 present time very little has been done in the application of exact 

 ecological methods to the study of the causes of change in plant 

 population. 



Past climates and climaxes are discussed from the basis of the paleo- 

 botanical literature. The author follows Saporta in distinguishing 

 four vegetation periods — The Eophytic, the Paleophytic, Mesophytic, 

 and Coenophytic. The works of Chamberlain and Salisbury, Hum- 

 phreys, Huntington, and Schuchert are used to establish the author's 

 conclusions. An extended review is given of changes of climate due 

 to deformation cycles, to volcanic activity, and to variations in sun- 

 spots. Climatic cycles are discussed at length. 



Succession during the Cenophytic era is termed the cenosere. The 



