Oct. 14, 1918 



Hardening Process in Plants 



95 



It is quite clear that the difference of about o.i degree in the freezing 

 point of the cell sap from hardened and nonhardened cabbages is insuf- 

 ficient to account for the resistance to low temperature shown by hard- 

 ened plants, for hardened plants are not injured by being frozen at a 

 temperature 3 degrees below the killing temperature for nonhardened 

 plants (6). Since ice formation takes place in this case, the freezing 

 point of the cell sap must be exceeded. 



CHEMICAL CHANGES DURING HARDENING 



Carbohydrates. — In studying the carbohydrate changes during the 

 hardening process cabbage plants from the same lot were placed part in 

 the greenhouse and part in a coldframe. The plants were allowed to 

 harden in the coldframe until they were not injured by being frozen 

 stiff at —3° C. Three samples of leaves, 25 gm. each, were taken from 

 each lot for starch and sugar determinations. The percentage values 

 are shown in Table III. 



Table III. — Analyses of carbohydrates in cabbage <^ 



a The writer is indebted to Mr. J. W. Kelly, of the Office of Drug-Plant, Poisonous Plant, Physiological 

 and Fermentation Investigations, for the carbohydrate determinations. 



In the average of these values it is seen that the equilibrium between 

 starch, glucose, and sucrose in the nonhardened plants in which poly- 

 saccharids predominate is displaced in hardened cabbages in the direc- 

 tion of the mono- and di-saccharids. Lidforss (sj) found this to be a 

 common transformation in plants during the cold season. Hasselbring 

 and Hawkins {18) have found a similar condition to occur in sweet 

 potatoes kept at low temperatures. They submit evidence to show 

 that the increase in sucrose takes place only after glucose formation 

 from the starch. It is difficult to maintain cabbage plants without 

 photosynthesis for a sufficient time to observe if that is the case here. 



