620 STATE BOARD OP AGRICULTURE. 



at the low moisture contentfs. represents actual concentration of solution 

 throws a new and important light on the subject of the wilting coeflfi- 

 eient of plants. The wilting of plants has heretofore been generally 

 attributed to their inability to take up the water which is held by the 

 soil with a great attractive force. While this explanation is undoubted- 

 ly correct and especially if it is true that some of the water is loosely 

 chemically combin»fl or physically adsorbed and consequently removed 

 from the liquid phase, yet if the great depression of the freezing point 

 at the low moisture content represents concentration of solution, then 

 the wilting of plants must be also influenced by plasmalytic phenomena. 

 Af> already seen, the calculated concentration amounts in some cases 

 to over 28,000 p. p. m., which is equivalent to an osmotic pressure of 

 over 12 atmos-phercs. At a still lower moisture content these magni- 

 tudes would be far greater. "When it is considered that the osmotic 

 pressure of the cell sap of such common agricultural plants as wheat, 

 barley, oats, corn, generally amounts to only about 5 atmospheres un- 

 der humid conditions then the possibility of the wilting of plants in 

 some soils at least being partly due to the plasmolytic phenomena, be- 

 comes greatly strengthened. Again, the best standard nutrient solu- 

 tions contain an osmotic pressure of only between 1.50 and 1.75 atmos- 

 pheres. Knops standard nutrient solution and the more recent one 

 proposed by Shive, (17), contain an osmotic pressure of 2.75 and 1.5 

 atmospheres, respectively. 



It would seem very possible, therefore, that in some soils at least, 

 especially in the complex types where the depression of the freezing 

 point is greatest, the concentration of the. solution probably plays a 

 very important part in the wilting of plants. 



Again, if the concentration of the soil solution varies tremendously 

 with the moisture content, then it becomes at once obvious that the centi- 

 fuge and paraffin oil methods can give some information concerning the 

 concentration of the soil solution only at the moisture content at which 

 the extraction can be made. Even at that moisture content, however, 

 the concentration of the extracted water is only approximately close 

 to the total concentration of the entire moisture in the soil, if the theo- 

 retical principles already discussed (p. G) are correct. 



Finally, it must be stated that the freezing point method with further 

 development promises of furnishing a quantitative comparison of the 

 soluble salt content in different soils and thereby give an idea as to 

 their degree of fertility. In its present stage it can only compare the- 

 concentration or salt content of the soil 'solution at different moisture 

 contents of the same soil, and between very extreme types of soil. The 

 moisture content seems to be the controlling factor and the develop- 

 ment of the method towards being employed to compare quantitatively 

 the salt content and probably the fertility of different soils, lies in 

 standardizing the moisture content, and this phase of the work is now 

 under investigation. 



(") Plant World, IQIS. 



