164 The Plant World 



entrance is due to lack of the resquite osmotic gradient, while 

 in the second it is probably due to properties of the absorbing 

 surfaces or osmotic membranes, the resquisite gradient, how- 

 ever, being present. 



Numerous fundamentally important considerations in Fit- 

 ting's highly admirable, though somewhat loosely presented, 

 researches, have received no mention at all in the present paper; 

 whoever is interested in the water relations of plants must 

 study the original, the author of which is to be congratulated 

 upon the success and thoroughness with which he has carried 

 out, under rather difficult conditions, what will long remain 

 a fundamental pioneer research not only for desert ecology but 

 also for ecology in general and for scientific agriculture. 



The Johns Ho(^\ins Uiihersiiy. 



vSTUDIES IN SOIL PHYSICS, IV. * 



The Physical Constants of Soils. 



E. E. Free. 



Soil science has begun its introduction to the quantitative, 

 and its votaries are newly but rapidly learning to"observe"a lit 

 tie less and to measure a little more and a little more accurately. 

 It is a much needed change — one of great promise and already 

 of some fiuition, but perhaps its greatest service has been to 

 call attention to the weaknesses of present methods and the in- 

 adequacy of present tools. There are so few measurements that 

 can be applied to problems of the soil. In soil physics, for in- 

 stance, we are accustomed to refer the various physical behav- 

 iors of the soil to a hypothetical "physical nature" or "physi- 

 cal character" which is supposed to be fundamental and causal 

 of all more superfical properties and behaviors. Whether we 

 call this physical character the "nature and numbers of the 

 constituent particles' ' or whether we define it more exactly 

 (and less luminously) as the expression of the possible ranges 

 of variation of all the physical properties, or whether we shirk 



*Publishcd by permission of the Secretary of Agriculture. 



