500 



Journal of Agricultural Research 



Vol. Xm, No. lo 



of those treated with toluene, its solubility being less than that of 

 chloroform. 



RELATIVE FREEZING POINT OF THE SAP OF DIFFERENT KINDS AND 

 VARIETIES OF GRAIN 



In this study different kinds of cereals known to vary widely in their 

 resistance to winter killing were selected. The first determination was 

 made on November 27, 191 5. The leaves were gathered between 8.15 

 and 9 a. m. The day was cool and cloudy, with an occasional light 

 shower. The leaves were treated with chloroform for 30 minutes. 

 Probably the depression is somewhat less than it would have been had 

 they been treated for a longer period. The sap was placed on ice as 

 soon as extracted, and left until the freezing point was determined. The 

 results are given in Table IV. The varieties are given in this and the 

 following tables in the order of their hardiness as shown by general 

 field experience. 



Table IV. — Relative freezing point of the sap of winter cereals on November 27, igi^ 



Kind of grain. 



Variety. 



Average. 



Rye {Secale cereale) 



Wheat 



Do 



Emmer {Triticum dicoccum) 



Barley 



Oats {Avena sativa) 



Kharkof 



Fultz 



Black Winter 



Tennessee Winter. 

 Culberson Winter. 



-1.044 

 -1.230 



— I. 076 



— I. 012 



— I. 117 

 -I. 199 



The data can scarcely be said to show a close relation between the 

 sap density and hardiness. Kharkof wheat, which is very hardy, shows 

 the greatest depression of the freezing point, but the depression for 

 Culberson oats, which is the least hardy of any of the winter cereals, is 

 almost as great. The depression for rye, which will survive greater 

 degrees of cold than any other cereal, is much less than for winter oats. 



A second determination was made on December 17 and 18, 191 5. 

 The leaves were gathered at 1.30 p. m. on the 17th, placed in air-tight 

 cans, and taken to the laboratory. They were then macerated in a 

 mortar, and the sap was filtered and placed on ice until the next day, 

 when the freezing point of each sample was determined. December 17 

 was clear and cold. The air temperature when the leaves were gathered 

 was — 16.9° C. (1.5° F.) and the soil temperature at a depth of i inch was 

 — 6.1° C. (21° F.). The leaves of many of the plants were badly wilted, 

 indicating inability to secure enough water from the cold and frozen soil 

 to supply that lost by transpiration. The results are presented in 

 Table V. 



