52 BOOKS AND CURRENT LITERATUEE 



fossil remains of plants are interpreted by a method of inference based 

 on the phylogenetic system. B}^ the occurrence of certain genera it is 

 inferred that the plant communities were of this or that well recog- 

 nized ecological character. By this method it is rather clearly indi- 

 cated that the advance of the ice sheet and the gradual change in the 

 climate led to the changes from hardwoods to conifers, from conifers 

 to shrubs, from shrubs to tundra, and from tundra to ice. This ad- 

 vance continued 'to the beginning of the reverse condition when ice 

 gave way to tundra, tundra to shrub, shrub to conifer, and conifer to 

 hardwood. Considerable attention is given to the successions in peat 

 bogs, since here is found a comparatively complete record of past suc- 

 cessions. 



The Mesophytic and Paleophytic eras are treated in much the same 

 way. The conclusions are reached largely by inference and seem 

 fairly well substantiated by the study of fossil remains and geological 

 structure. 



The author has succeeded in bringing together into one volume an 

 immense amount of information with respect to plant succession and 

 has developed a system of nomenclature and classification far in ad- 

 vance of any heretofore employed. In putting the study of vegetation 

 on a successional basis the author has avoided the difficulty previously 

 experienced of having to deal with static and successional phenomena 

 in separate systems. The present system is pliable enough to admit 

 of the ready placing of vegetation types which are rapidly changing, 

 and also of types which are relatively stable. Absolute climax types 

 are doubtless nonexistent but the relative climax shown in many of 

 our types of vegetation can be fitted into this system without mis- 

 understanding. With this comprehensive discussion as a starting 

 point, a study of succession, either primary or secondary, should be 

 made in which each stage is fully anal.yzed and the physical conditions 

 adequately measured with instrumental methods far more complete 

 and thorough than any yet proposed, in which the causes of changes 

 of type can be explained by accurately measured changes in the en- 

 vironment — a study combining physical methods and vegetation 

 methods in which the instrumental data are actually presented to 

 prove the changes which are indicated by the vegetation. In short, 

 a real instrumental and vegetational analysis of a succession should 

 be made, which will make clear the physical or chemical basis of each 

 vegetational change. This must be done by a man on the ground and 

 with the application of far more exact methods than those at present 



