256 Forestry Quarterly. 



dead plants and that the Hmit is reached only when the soil mois- 

 ture comes into approximate equilibrium with the moisture con- 

 tent of the air. While from a physical standpoint such water 

 may be considered available to the plant, yet from the physio- 

 logical standpoint it is non-available, since no vital process, no 

 growth at least, takes place when the leaves are permanently 

 wilted. The authors also found that the wilting coefficient is not 

 materially influenced by the dryness of the air, by moderate 

 changes in solar intensity or by differences in the amount of soil 

 moisture available during the period of growth. The latter 

 means that when plants constantly supplied with varying amounts 

 of moisture during the growing period were allowed to dry out, 

 the amount of moisture in the soil at the wilting point was practi- 

 cally the same in each case. 



Certain points made by the authors do not seem clear to the 

 reviewer. For example, on page 21 one reads that the soil mois- 

 ture content at the wilting point is not dependent to any material 

 degree on the age of the plant. Yet on page 56 the authors state 

 that the differences observed in the wilting coefficient for different 

 plants are largely due to the more perfect root distribution of one 

 variety as compared with another. Certainly the root distribution 

 of a plant varies from the seedling stage to maturity. If such 

 variation in mature plants of different species brings about a 

 variation in the wilting coefficient, it would seem that a variation 

 in the root distribution of a single plant at various stages of its 

 development would produce similar results. 



Under the discussion of indirect methods of determining the 

 wilting coefficient, the authors give formulae to determine such 

 coefficient when such things as the moisture equivalent, the 

 hygroscopic coefficient, the saturation coefficient and the soil tex- 

 ture are known. 



The experiments described in the bulletin were made with a 

 great variety of cultivated plants. Similar experiments with tree 

 seedlings are very much to be desired. 



C. D. H. 



The Forest Conditions of the Ozark Region of Missouri. By 

 Samuel J. Record. Bulletin 89, Missouri Agricultural Experi- 

 ment Station. Columbia, Mo. 191 1. 



