R. A. G ortner, J. V. Lawrence and J. A. Harris 141 



In no instance did a first sample of sap, pressed from unfrozen 

 tissue, give a depression of the freezing point as great as that from 

 the " original f rozen sample." Generally, all the f ractions extracted 

 by pressing alone show less depression of the freezing point than 

 does the juice extracted from the " original f rozen tissue." In some 

 cases, however, the later samples of a series are as concentrated as, 

 or more concentrated than, the sap of the " original frozen sample." 

 Diagram i (Plate i) gives an Illustration of this case. 



Dixon and Atkins, in referring to the results of their own work 

 and to the evidence obtained incidentally by others, mention only 

 higher concentrations of the later samples. In general it is true that 

 successive samples become more concentrated. The regularity of 

 this increase in concentration is admirably shown by Diagram i or 2 

 ( Plate I ) . Such is, however, not always the case. In some instances 

 the fluid extracted by continuous pressing, without rearrangement 

 of the tissue-mass, may become less and less concentrated. This is 

 seen, for example, in the series of extractions from cabbage leaves 

 shown in Diagram 3 (Plate i). In other instances all of the f rac- 

 tions may be of about the same concentration, as is shown in Dia- 

 gram 4 (Plate i). 



The juice obtained from the " frozen residue " always, so far 

 as our experience goes, shows a greater osmotic pressure than that 

 for any of the samples extracted by direct pressing or for the juice 

 from the " original frozen sample." Both of these conditions are to 

 be expected from the fact that the individual fractions of sap ob- 

 tained by pressure of the tissue-mass are almost invariably less con- 

 centrated than that from the " original frozen sample," and on the 

 average are always so. We are not convinced, however, that the high 

 values for the depression of the freezing point of the sap from the 

 "frozen residue" may not be due, in part, to chemical changes 

 occurring during the process of pressing. 



Thus, the resuks secured fully substantiate the conclusions of 

 Dixon and Atkins, that samples of sap pressed from unfrozen tis- 

 sues cannot be taken as typical of the original concentration of the 

 Juices in the tissues. While the entire credit for this advance in the 

 study of vegetable saps must, with the exceptions noted in their 



