lo6 Journal of Agricultural Research voi. xv, no. 2 



showed that conduction of food materials occurred after the plasmolysis 



of these conducting cells. The protoplasmic connection between cells is, 



therefore, not necessarily broken by plasmolysis, according to the 



evidence above cited. Consequently it is necessary to assume that in 



some manner these strands are killed on plasmolysis if the growth 



stimulus is attributed to the removal of correlation factors and the 



breaking of protoplasmic connection between the cells. 



It is entirely possible that the strands running to the cell wall in 



plasmolysed cells may remain alive, since they are scarcely thinner than 



the plasmodesmen themselves. In this case the "living continuity" is 



not broken. It is equally possible that they are killed, and in such case 



death may be due to changes in the state of the protoplasm constituents 



owing to changed acidity and an increase in the concentration of the 



salts. If these threads are killed on plasmolysis of the cells, equal 



changes can be expected to occur on the surface of the protoplast. It 



was Chandler's idea that — 



killing from cold is more likely a mechanical injury due to the withdrawal of water 

 from the protoplasmic membrane than an injury resulting from a precipitation of 

 proteins. 



The effect of plasmolysis on the regeneration of plasmolyzed cells can 

 then be ascribed also to this change in the membrane as well as to the 

 removal of the correlation effect. If growth is due to the removal of 

 the correlation effect through plasmolysis of the cells on freezing then 

 one would expect the plasmolyzed cells of the hardened cabbages to be 

 stimulated to growth in the same manner as those of nonhardened 

 cabbages. But this does not occur; consequently the renewal of growth 

 in the cells can not be ascribed to the breaking of the living continuity and 

 removal of the correlation effect in the case of the cabbage. The lack 

 of growth in the cells of hardened cabbages is evidently due to their 

 inability to withstand the concentration of the cell sap and increased 

 acidity without injury. 



It appears that in the process of hardening there are changes which 

 occur in the proteins. To these changes the greatest effect of the hard- 

 ening is to be ascribed. The changes are cleavages to simple forms if the 

 increase of amino acids on hardening of the plants is taken as an indi- 

 cation. The simple forms of the proteins are not so easily precipitated 

 by freezing or by the addition of acid as the more complex foims. The 

 increase of acidity of a plant juice on freezing is accompanied by an 

 increase in the concentration of the salts. Both conditions are favorable 

 for protein precipitation. 



The surface layer is the most exposed part of the plasmolyzed proto- 

 plast. It is therefore probable that the greatest changes in aggiegation 

 of the proteins occur there. 



The change in color of coleus leaves after freezing indicates that 

 through irreversible combination with the proteins the excess hydro- 



