THE METHOD OF MOVEMENT 153 



concentrations than the supplying cells. Fernald (1925) 

 found that the osmotic concentration near the growing 

 point of rapidly growing shoots was distinctly higher than 

 that of the leaves which were obviously supplying the foods 

 necessary for growth. In potato tubers also, the osmotic 

 concentrations of the sprouts were regularly much higher 

 than those of the tuber from which the foods were coming. 

 Although this evidence seems fairly conclusive, that receiv- 

 ing tissues may have higher osmotic concentrations than 

 the supplying tissues, certain doubts may arise concerning 

 it. Fernald's freezing-point determinations were made 

 with sap that was first extracted from the tissues, but Car- 

 rick (1924) has given evidence showing that the freezing 

 point of extracted sap or of killed tissue is likely to be very 

 different from that of the living tissue. Although the 

 younger tissues which had the higher concentrations 

 were chiefly growing tissues and therefore were receiving 

 materials from the older leaves or storage tissues, they also 

 included some cells that were perhaps mature, and, fur- 

 thermore, no precautions were taken to exclude light so the 

 possibility of photosynthesis, especially in the leafy stems 

 which were exposed to full light, may have partly accounted 

 for the high concentrations in the younger parts. 



In order to test more critically the possible bearing of an 

 osmotic gradient upon the Miinch hypothesis, we have 

 grown various types of material in complete darkness so 

 as to insure a transport from storage tissues to receiving 

 tissues (Curtis and Scofield, 1933). The osmotic concen- 

 trations have been determined in three different ways. 

 The freezing points of the tissues have been determined 

 directly by inserting thermocouples into the tissues to be 

 tested. This made it possible to determine the freezing 

 point without first killing the tissue or extracting its sap, 

 and also to restrict the determinations to younger, more 

 nearly meristematic regions. Freezing-point determina- 

 tions were also made on samples of extracted sap. With 

 onion tissue the osmotic concentrations were also estimated 

 by the plasmolytic method, using sucrose as the plasmo- 



