BOOKS AND CURRENT LITERATURE 361 



tion of the fact that future research must deal with the complex of 

 reactions and the exact role of each factor in the complex. The re- 

 viewer^ has already emphasized these requirements of successional 

 research, and it may be helpful to point out here the essentials of 

 thorough-going quantitative study. It is obvious that the reaction- 

 level, in which the seedlings of dominants occur, must be the main 

 objective. In most cases, measurements of water-content and evapora- 

 tion, and of light in the reaction-level of the various zones or stages 

 will suffice, but all of these must be dealt with in the same investigation. 

 ' In the oxysere, aeration and other factors must be studied, while in the 

 halosere the chief attention must be given to the solutes. It is already 

 apparent however that we must soon use the plant as an index of re- 

 action. The transpiration of each dominant will prove by far the best 

 measure of the control of water reactions, just as the amount of pho- 

 tosynthate and growth will be the best measure of serai response to 

 light reactions. Perhaps the greatest need in the study of succession is 

 the use of methods of sequence and experiment in place of the almost 

 universal method of inference. It seems mevitable that the next 

 great step in advance will be made by series of reaction quadrats, 

 in which the interplay of development and reaction may be followed 

 year by year, and where the actual fate of dominants can be checked 

 by reciprocal experunents in ecesis. — Frederic E. Clements. 



Soil Temperature and Plant Growth. — The effects of soil tem- 

 perature per se, as distinguished from that of the air, on the growth and 

 development of plants, appears not to have received very much atten- 

 tion. The recent study by Halsted and Waksman^ therefore, is of 

 much interest. In this research two lots of corn were placed under 

 observation. Of these one lot was grown between July 30 and August 

 26, and the other between October 29 and November 29, in a green- 

 house which was not artificially heated. The temperature of the soil 

 was noted twice daily, at 6 o'clock, morning and evening. For the 

 summer the average temperature of the soil was 25.68°C. In the 

 autumn the daily average was 12.87°C. The air temperatures are 

 not given. 



The title of the study does not give the idea that it is on heredity, 



5 Clements, F. E. Plant Succession. Carnegie Inst. Wash. Pub. 1916. Pp. 

 96, 421. 



1 Halsted, B. D., and Waksman, S. A. The Influence of Soil Temperature 

 upon Seedling Corn. Soil Science 3: 393-398, 1917. 



