RELATION OF THE DENSITY OF CELL SAP TO WINTER 

 HARDINESS IN SMALL GRAINS^ 



By S. C. Sai^mon, Professor of Farm Crops, and F. L. Fleming, Department of Agron- 

 omy, Kansas Agricultural Experiment Station 



INTRODUCTION 



Theoretical considerations suggest a close relation between the density 

 of the cell sap and the ability of plants to survive low temperatures. If 

 death from cold be due to the formation of ice in the plant tissue, to 

 physiological drouth, to the precipitation of the proteids of the proto- 

 plasm, or the dessiccation of the protoplasm, then an increase in the 

 electrolytic contents of the sap would increase the hardiness either by 

 lowering the freezing point of the sap or by reducing transpiration. 



These considerations led to a study of the sap density of various small 

 grains as one phase of a series of investigations conducted to determine 

 the causes of winter-killing. The work was done during the fall and 

 winter seasons of 191 5-1 6 and 191 6-1 7. Practically all of the actual 

 determinations were made by the junior writer. 



EXPERIMENTAL METHODS 



The experiments reported in this paper were confined to the winter ce- 

 reals, rye, wheat, emmer, barley, and oats, which, as shown by general field 

 experience, decrease in comparative winter hardiness in the order named. 



Much time was consumed in working out a suitable technic, especially 

 for the extraction of the cell sap. Maceration of the tissue is generally 

 unsatisfactory without a means for centrifuging the sap. As pointed out 

 by Dixon and Atkins,^ the freezing point of sap extracted without previous 

 treatment of the tissue is likely to be too low. Liquid air was not avail- 

 able for rendering the plasma membrane permeable, as suggested by Dixon 

 and Atkins; hence, we resorted to chemical reagents. For this purpose 

 toluene and chloroform vapor were employed. 



This method is not entirely satisfactory because of the slight solubiUty 

 of these reagents and the opportunity for changes in the cell sap during 

 the rather long period of treatment that is necessary. However, it is 

 beUeved the methods finally worked out circumvent these objections in 

 a large degree, and that the experimental errors involved are too small to 

 affect the conclusions reached in this investigation. 



All determinations were from the leaves of plants sowed the last 

 week in September or the first week m October. The samples were 

 gathered in duplicate, placed immediately in air-tight cans, and taken 

 to the laboratory. All lots for any one experiment were gathered at the 



1 Contribution 15 from the Department of Agronomy, Kansas Agricultural Experiment Station. 



2 Dixon, H. H., and Atkins. W. R. G. osmotic pressures in plants, i. methods of extracting 

 SAP FROM PLANT organs. In Notcs Bot. School, Trinity Coll., Dublin, v. 2, n'o. 4. P- 154-176. 1913- 



Journal of Agricultural Research, Vol. XIII, No. 10 



Washmgton. D. C. June3. 191S 



Key No. Kans.-i2 



(497) 



