94 



Journal oj Agricultural Research 



Vol. XV, No. 3 



eating that they rapidly pass through some sort of maturation process. 

 The more common injury to the cells about the veins indicates that there 

 is a physiological difference between the vascular tissue and the other 

 cells of the leaf. This physiological difference is suggested also by 

 Mangham (27) in a recent article. 



FREEZING POINT AND EXPRESSION OF CABBAGE JUICES 



A large number of determinations were made of the freezing points 

 of juice expressed by different methods from hardened and nonhardened 

 plants. As Dixon and Atkins (<?) have shown, the method of treatment 

 before expression has a considerable influence on the depression values. 

 However, there is about the same difference between the freezing points 

 of juices expressed from hardened and nonhardened cabbages regardless 

 of the method of treatment before expression. Tests were made after 

 freezing in liquid air, after freezing with solid carbon dioxid, after freezing 

 at —5° C, and without freezing. One of the most convenient methods 

 is to freeze the tissue with carbon dioxid until brittle and then to grind 

 it in a mortar to a fine powder. The material can then be transferred 

 to the press and allowed to thaw out. This method is more available 

 than the liquid-air method and is less expensive. The sap was expressed 

 either in a large hand press which left a marc practically dry or in a 

 hydraulic press under a pressure of 10 to 30 tons on a 2>^-inch ram. 

 Table II gives the comparative values. 



Average excess depression of hardened over nonhardened, o.o8s°C. 



The smallest difference, 0.036° C, shown after freezing at —5° may 

 be due to a greater injury to the nonhardened leaves and corresponding 

 increase in concentration of the expressed juice. The increase of the 

 freezing-point depression on treatment with solid carbon dioxid and 

 liquid air over that given by freezing at — 5° may be due to changes in 

 the cell membranes which make them more permeable to qsmotically 

 active substances. The process of freezing, especially to this degree, is no 

 innocent procedure and may result in changes which produce protein pre- 

 cipitation. Consequently, juices expressed in this manner do not repre- 

 sent the true concentration of the cell sap for all its constituents. 



