Killing of Plant Tissue by Low Temperature 183 



This is, of course, assuming that the eutectic point of the solu- 

 tion is below these temperatures. It also assumes that the freezing 

 point is lowered exactly in proportion to the molar concentration 

 of the solution; that is, if there be four gram molecules in a liter of 

 water, the freezing point should be four times -1.86 C. This is 

 probably not quite true but the difference is so slight that it may be 

 ignored here. It will thus be seen that with a solution in which 

 there is a gram molecule to a liter of water of a solute that stays 

 in solution below -29.76 C, there would be as much water unfrozen 

 at -14.88 C, as there would be at -29.76 C, if the molar concentra- 

 tion is only half as great. 



Maximow concludes that the protective action of the material 

 he used was greater than could be explained by the depression of the 

 freezing point of the sap. He may not have considered the above 

 facts. Another fact should be considered. With the plants Maxi- 

 mow used, possibly a large percentage of the sap solute crystallized 

 out at temperatures considerably above the minimum temperatures 

 that he used. Maximow used as a protective substance a solution 

 of equal density with the plant sap and with a low eutectic 

 point, then at a temperature of say -10 C, it would be considerably 

 more dense than the plant sap from which crystallization had taken 

 place. While theoretically the protective action of increased den- 

 sity should be greater with plants that kill at a rather low tempera- 

 ture like winter buds and wood, we have found no way to demonstrate 

 such protective action with such tissue. The only means of increas- 

 ing the sap density of such tissue that suggested itself to us was by 

 applying fertilizers like potassium chloride to the soil and this method 

 has not had that effect. 



From the experience of Maximow and experience here with 

 cabbage and other plants where the salts in solution have increased 

 the resistance to cold as much as it was increased by organic com- 

 pounds, and in some cases more, it seems that one is safe in conclud- 

 ing 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 the precipitation of proteids as suggested by 

 Gorke, since an increase in the percentage of any mineral salt should 

 tend to hasten the precipitation of proteids rather than reduce it. 



It seemed that one good test of the theory of Gorke^ would be 

 to find whether or not a lower temperature is required to precipitate 

 proteids from the sap of twigs as they increase in hardiness during 



'Landw. Vorauchs. Vol. 65. p. 149, 190G. (Hlbl. No 17). 



