Oct. 14, 1918 



Hardening Process in Plants 



91 



Table I shows the plasmolytic Umit concentrations after 30 minutes' 

 exposure. 



Table I. — Plasmolytic limit concentrations for normal and tumor cells 



These values are for young tumors about 5 days old and in active 

 growth. The age of the tumor has much to do with its plasmolytic 

 behavior. Very old tumor cells which have stopped growth show no 

 difference in plasmolytic behavior from normal jaesophyll cells of the 

 same leaf. The writer is inclined to regard the difference in the plas- 

 molytic behavior as being due, not to a difference in the osmotic concen- 

 tration of the cell sap, but rather to differences in permeability, espe- 

 cially to water, and probably also to the substance used for plasmol- 

 ysis. Smith {45, p. 184) says: 



... it would seem . . . that in local osmotic action (possibly in some stages chemical 

 action also) of various substances ... we have . . . the explanation of tumor 

 growth. . . . 



This statement evidently implies a changed permeability as well as 

 pure osmotic effect. The writer has determined the freezing points of 

 juices expressed from cultures of tumors caused by Bacillus tumejaciens 

 grown on daisy from Smith's cultures, and has found a lower freezing 

 point for tumor tissue than for either stem or leaf tissue. Evidence 

 offered by the greater freezing-point depression of saps of parasites than 

 of saps from the host {17) seem to indicate that such an excess depression 

 is a common condition for parasitic tissues (24). The accumulation of 

 such large quantities of sugar in the tumors of cabbage caused by freezing 

 leads the author to believe that there is some change in the cells which 

 allows them to obtain it from theij neighbors in the siuromiding areas. 

 The quantities of starch present in the cells before freezing are not 

 sufficient to account for this much sugar, for the yoimg leaves in which 

 tumors develop rapidly contain very little starch. The decrease in 

 chlorophyll would hardly be in accord with the synthesis of the sugar 

 within the tumor cells. 



It is probable that in the frozen cells of the injected areas there occur 



changes in the state of the protoplasm constitutents so that more sugar 



is adsorbed there, or so that the sugar is held there in some sort of 



chemical combination. Osterhout {40) suggests that differences in 



78774°— 18 3 



