498 



Journal of Agricultural Research 



Vol. XIII, No. lo 



same time of day and with the same conditions, as far as possible. In all 

 cases, except when otherwise noted, the leaves were placed on ice or in a 

 refrigerator at a temperature of 4° to 5° C. The extracted sap was kept 

 on ice in tightly stoppered bottles, or in a refrigerator until a determi- 

 nation of the freezing point was made. 



The freezing point was determined with a Beckman thermometer and 

 the usual freezing-point apparatus, except that a tube somewhat smaller 

 than usual was employed so that only a small quantity of sap (5-6 c. c.) 

 was necessary for a determination. 



The sap was extracted by pressure applied to the leaves which were 

 first macerated, or treated with chloroform or toluene, as indicated. 



EFFECT OF TIME OF TREATMENT ON DENSITY OF EXTRACTED SAP 



In practically all cases in which different varieties or kinds of grain, 

 were compared, determinations were made in duplicate, and in nearly 

 all cases considerable variation between duplicate samples was found. 

 At first this was thought to be due to imperfect extraction of the sap. 

 Since the sap first expressed has a lower density than that extracted 

 later, as shown by Dixon and Atkins and confirmed by us, imperfect 

 extraction might have considerable effect on the density. To avoid this 

 error, experiments were conducted in which the leaves were treated for 

 various periods with chloroform or toluene. Wheat {Triticum spp.) 

 leaves were used in the experiments with chloroform, and wheat and 

 barley (Hordeum spp.) leaves in those with toluene. In part of the 

 experiments with chloroform duplicate samples were kept during treat- 

 ment at both room temperature and in an ice box at a temperature of 

 4° to 5° C. The results are shown in Tables I and II. 



Table; I. 



-Effect on sap density of treating wheat with chloroform for different periods 

 and at different temperatures 



