lo8 Journal of Agricultural Research vo1.xv,no.8 



(6) The principal effect of the hardening process for cabbages is a 

 change in the constituents of the protoplasm which prevent their pre- 

 cipitation as a result of the physical changes incident upon freezing. The 

 proteins are changed to forms which are less easily precipitated. This 

 is indicated by an increase in the amino-acid content of the cabbage 

 plants on hardening. 



(7) The factors which produce protein precipitation on the freezing 

 of a plant juice are held to be principally the increase in the hydrogen-ion 

 concentration and the increase in the concentration of the salts. The 

 latter factor is held to be insufficient to cause precipitation except under 

 the conditions of a changed acidity. Cabbage plants were found to 

 become resistant to a half-hour's freezing at —3° C. after exposure to 

 -f 3° for five days. During this time the carbohydrate changes were 

 slight. Hence, the prevention of protein precipitation by sugar accumu- 

 lated during haidening is not sufficient to account for the resistance of 

 hardened plants to freezing. 



(8) The proteins of the midrib of cabbage leaves are precipitated more 

 readily than those from the rest of the leaf. This is considered to be due 

 to physiological differences between vascular tissues and the other 

 tissues of the leaf. 



(9) In juices of nonhardened and hardened cabbages the proteins of 

 the former were found to be precipitated to a greater degree by freezing 

 than those of the latter. The percentage of precipitation for such juices 

 on freezing is closely paralleled by the relative precipitation on the 

 addition of acid. 



(10) The greatest changes induced by freezing are supposed to occur 

 n the outer portions of the protoplast since this is most exposed on 

 plasmolysis. 



(11) The effects of desiccation, freezing, and plasmolysis are considered 

 to be similar, in that all these processes cause changes in the hydrogen-ion 

 and salt concentrations. 



LITERATURE CITED 

 (i) Bartetzko, Hugo. 



1909. UNTERSUCHUNGEN UBER DAS ERFRIEREN VON SCHIMMELPItZEN. In 



Jahrb. Wiss. Bot., Bd. 47, Heft i, p. 57-98. 



(2) BiGELOW, S. E., and Rykenboer, E. A. 



1917. CAPILLARY PHENOMENA AND SXJPERCOOUNG. In Jour. Phys. Chem., V. 

 31, no. 6, p. 474-512, 8 fig. 



(3) BoviE, W. T. 



I915. A DIRECT READING POTENTIOMETER FOR MEASURING AND RECORDING 

 BOTH THE ACTUAL AND THE TOTAL REACTION OP SOLUTIONS. In Jour. 



Med. Research, v. ;^^ (n. s. v. 28), no. 2, p. 295 -322, 4 fig. 



- (4) BUNZELL, H. H. 



I914. A SIMPLIFIED AND INEXPENSIVE OXIDASE APPARATUS. In Jour. Biol. 



Chem., V. 17, no. 3, p. 409-411, i fig. 



