April 6, 1917] 



SCIENCE 



341 



The investigations of Douglas on " Weather 

 Cycles in the Growth of Big Trees " and " A 

 Method of Estimating Eainf all by the Growth 

 of Trees," of Huntington on the climatic 

 factor, and of Humphreys on the relation of 

 volcanic dust to climatic changes, etc., ap- 

 pear to have been the chief inspiration and 

 sources for this particular portion of the 

 monograph. 



This is a very new field for the modern 

 student of plant succession. The author states 

 that : " The interpretations of past vegetations 

 rests upon two basic assumptions. The first 

 is that the operation of climatic and topo- 

 graphic forces in moulding plant life has been 

 essentially the same throughout the various 

 geological periods. This is a direct corollary 

 of the conclusions of Lyell as to geology, and 

 of Huntington, Humphreys and others as to 

 climatology. The second assiunption is the 

 one already quoted, namely, that the operation 

 of succession as the developmental process in 

 vegetation has been essentially uniform 

 throughout the whole course of the geosere. 

 From these two assiunptions naturally follows 

 a third to the effect that the responses of ani- 

 mals and man to climate and to vegetation, 

 both as individuals and in groups, have re- 

 mained more or less identical throughout geo- 

 logical time. As a consequence of Darwin's 

 work, this has long been accepted for the indi- 

 vidual, but as to the community it still awaits 

 detailed confirmation by the new methods of 

 zoecology. Further, if all these be accepted 

 as necessary working hypotheses, it is evi- 

 dent that what is true of the parts must be 

 true of the whole plexus of geological causes 

 and biological responses in the past." 



The attempt is then made to trace the suc- 

 cessions through the various geological eras 

 with their shifting climates and climaxes. 

 But here again the details are so numerous 

 and so many biological principles are involved 

 that only first-hand examination of these 

 chapters can give the reader an adequate con- 

 ception of the matter handled in this way. In 

 passing it is interesting to note that Clements 

 ihas used vegetation rather than animal life 

 as the basis for the recognition of eras of the 



geological record, somewhat after the fashion 

 of Saporta (1881). Thus we read: Eophytic, 

 Paleophytic, Mesophytic, Cenophytic. 



These latter chapters should be particularly 

 suggestive and stimulating to the animal ecol- 

 ogist and the paleo-ecologist as well as to 

 others with an interest in the phenomena of 

 living thing of past ages. 



The bibliography of nearly a thousand titles, 

 the most of which have been abstracted or 

 noted somewhere in the text, is still another 

 valuable part of the book. This is probably 

 the most nearly complete collection of titles 

 on succession and related phenomena avail- 

 able. 



It may be said, after securing a bird's-eye 

 view of the book as a whole, that Clements's 

 monograph presents an invaluable summary 

 of our knowledge of plant succession and that 

 it must become at once the indispensable 

 reference and guide for the student of vege- 

 tative cycles in all parts of the world. 



Eaymond J. Pool 

 The Univeksity of Nebraska 



SPECIAL ARTICLES 



RECENT INVESTIGATIONS OF TRACTIVE RE- 

 SISTANCES TO MOTOR TRUCKS ON 

 ROADS AND PAVEMENTS 



An experimental investigation was carried 

 on in the research division of the electrical 

 engineering department, at the Massachusetts 

 Institute of Technology, during the year 

 1915, under a fund contributed for researches 

 on motor trucks, for the purpose of determin- 

 ing the tractive resistance of a motor delivery 

 wagon with four wheels and solid rubber 

 tires on various level urban roads and pave- 

 ments. The complete report on this research 

 was published in the Proceedings of the Amer- 

 ican Institute of Electrical Engineers, June, 

 1916. 



By " tractive resistance " is meant the hori- 

 zontal force necessary to apply to the truck 

 in order to keep it at a constant speed in still 

 air after deducting axle frictions and internal- 

 mechanism losses. It is, therefore, the re- 

 active force offered by the truck, assumed 



