NOTES ON THE TECHNIQUE OF THE DETERiAIINA- 



TION OF THE DEPRESSION OF THE FREEZING 



POINT OF VEGETABLE SAPS 



ROSS AIKEN GORTNER AND J. ARTHUR HARRIS 



Station for Experimentol Evolution, Cold Spring Harbor, .V. Y. 



During the summer of 1912 and 1913 we found it necessary to 

 carry out very extensive series of the observations needed in the 

 determination of certain of the physico-chemical constants of 

 vegetable juices. Since such work is receiving constantly in- 

 creasing attention — as is attested by the Symposium on Per- 

 meability and Osmotic Pressure before the Botanical Society of 

 America at the Cleveland meeting, the papers of which have been 

 published in this journal — it may not be out of place to state 

 some of the results of our experience in the routine of such deter- 

 minations. This seems the more desirable because of the fact 

 that manj?- of those who may wish to undertake such work are 

 unacquainted with some of the precautions necessary in even the 

 rough physico-chemical work possible with vegetable and animal 

 juices. 



The first step is the collection of the samples of sap. Up until 

 the last few months workers have almost invariably, if not always, 

 done this by pressing the fresh material with or \\»ithout anteced- 

 ent grinding. Some have used agate mortars to avoid possible 

 influence of the metal, but most have employed an ordinary metal 

 press. But in February, 191.3, Dixon and Atkins^ pointed out 

 that extractions representing much more accurately the solutes 

 of the whole tissue (because containing a much larger proportion 

 of the sap from the smaller vacuoles) could be made by freezing 

 the tissues to increase their permeability. 



This suggestion, which they have tested with thoroughness, 

 is undoubtedly of great importance. We doubt whether the 



1 Dixon, H. H. and W. R. G. Atkins, Sci. Proc. Roy. Dublin Soc. n. s. 13: 422- 

 433. 1913. 



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