610 



SCIENCE 



[N. S. Vol. LII. No. 1356 



etc. ... In the case of use or practise indicators, 

 the sequence differs in accordance with the nature 

 of the crop. When the crop is a natural one as in 

 grazing, the sequence is simple and direct. . . . 

 "With forage and grain crops, the sequence is more 

 complex, partly because the species concerned are 

 not native, but largely because the physical con- 

 ditions are unnatural as well as controlled. . . . 



... It is necessary to recognize that every dom- 

 inant can be used as an indicator of past and fu- 

 ture as well as of present conditions. This is 

 due, of course, to the fact that every dominant or 

 subdominant has a definite position in succes- 

 sion. . . . 



Bases and criteria are treated (pages 35-75) 

 ■under tlie following main headings : The 

 Physical Basis, The Physiological Basis, The 

 Associational Basis, The Suceessional Basis, 

 Indicator Criteria, Life-forms, Habitat-forms, 

 Growth-forms, and Communities as Indi- 

 cators. 



The third chapter (pages 76-104) deals 

 with the kinds of indicators, which are classi- 

 fied as Factor Indicators, Process Indicators 

 and Practise Indicators. Among the factors 

 considered are water, light, temperature and 

 solutes. In this connection, the author con- 

 siders lack of oxygen as the most important 

 factor aifecting plant growth in acid soils. 

 Discussing climatic and edaphic (soil) indi- 

 cators, it is stated: 



The local or edaphic conditions find their ex- 

 pression in the serai dominants and subdominants, 

 and the communities which they constitute. The 

 widespread climatic conditions are reflected in the 

 climax formation, associations, and societies. 



Process indicators belong to suceessional 

 rather than to climax associations and indi- 

 cate the effects of disturbances of the habitat, 

 either " natural " or brought about by the 

 agency of man. Practise indicators show 

 whether the land is suitable for agriculture, 

 grazing, or forestry, and with less certainty, 

 to what kinds of crop and methods of pro- 

 duction it is best adapted. 



A large part of the book (pages 105-236) is 

 devoted to descriptions of the climax forma- 

 tions of western Worth America, comprising 



the various associations of grassland, scrub- 

 land or chaparral and forest. 



Agricultural indicators are discussed on 

 pages 237-269. Here the author develops his 

 ideas as to the classification of the remaining 

 public land on an indicator plant basis, 

 stating : 



... it should become a cardinal principle of 

 land classification to rate as grazing or forest 

 land all areas in which it is impossible to pro- 

 duce an average crop three years out of four. 

 This would insure an adequate and permanent de- 

 velopment of agriculture wherever possible and 

 would warrant the introduction of scientific and 

 economic systems of grazing, which would change 

 it from a game of chance into an industry. 



The subject of grazing indicators is treated 

 at greater length (pages 270-335), the author 

 pointing out that, " the simplest and most ob- 

 vious indication of a plant community is that 

 which denotes the possibility of grazing." In 

 regard to the carrying capacity of range land, 

 it is stated: 



With respect to the plant cover alone, the 

 carrying capacity of a grazing type is summed up 

 in the total amount of the annual crop of forage, 

 but the total yield must be interpreted in terms 

 of value and utilization. Hence, it is necessary to 

 take into account the composition of the type, the 

 palatability and nutritive value of the dominants 

 and subdominants, the duration and timeliness of 

 the grazing season, and the effects of the climax 

 cycle. 



Forest indicators are discussed on pages 

 336-363, and the book closes with an exten- 

 sive bibliography. 



Field investigations extending over many 

 years and covering practically the whole of 

 the western United States have fitted Dr. 

 Clements to deal with his topic in a com- 

 prehensive and illuminating manner. The 

 philosophical point of view is predominant 

 throughout the work, and the relation of the 

 subject to other branches of science, as well 

 as to practical affairs, is convincingly pre- 

 sented. The care used in preparing this 

 handsome volume and its numerous excellent 

 illustrations deserves high commendation. 



Thomas H. Kearney 



