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BRIEFER ARTICLES 



USE OF DILATOMETER IN STUDYING SOIL AND PLANT 



RELATIONSHIPS 



The dilatometer was used successfully by Bouyoucos 1 in studying 

 the forms of water in soils, and in studying the freezing point lowerings 

 of soils and plants, McCool and Millar 2 observed that the time of 

 day when samples of plants were taken markedly influenced the freezing 

 point low r erings of the leaves. The density of the sap was found to 

 increase from morning until noon, and again decrease in the afternoon, 

 reaching its lowest point at night. By means of the dilatometer the 

 amount of water that froze readily was less at noon than in the morning, 

 the freezing point lowerings apparently being governed somewhat by 

 the form of water in the tissues. 



We have repeated some of the experiments that were previously 

 reported, and obtained additional information by means of the dilatom- 

 eter. There are certain precautions that should be taken in making 

 determinations of the amount of water that freezes in plant tissues by 

 means of the dilatometer. 



The sample is quickly weighed, inserted into the bowl of the dila- 

 tometer, and ligroin added. It is advisable to remove air bubbles 

 either by shaking or by means of a suction pump. Where a bath of 

 about — i . 5 C. is employed, 10 gm. of the tissue may be used; but with 

 colder baths, such as —4 or —6° C, it is imperative that much smaller 

 quantities of tissue be added to the dilatometer, in order that super- 







cooling may be brought about. With some plants 2 gm. are ample, while 

 with others somewhat larger amounts may be employed to advantage. It 

 is very difficult to accomplish supercooling if the freezing mixture or the 

 dilatometer is agitated while the temperature of the material is being 

 lowered. When equilibrium has been attained, solidification may be 

 accomplished readily by agitating the dilatometer. 



Several plants have been employed, namely, rye, wheat, corn, sweet 

 clover, and red clover. They were grown on fertilized and untreated 



1 Tech. Bull. no. 36, Mich. Exper. Sta. 



2 The water content of the soil and the composition and concentration of the soil 

 solution as indicated by the freezing point lowerings of the roots and tops of plants. 

 Soil Sci. 3:113-138. 1917. 





3*7) 



[Botanical Gazette, vol. 70 



