WINTER KILLING AND HARDINESS 255 



greater density there was greater hardiness. Unfortunately, attempts 

 to increase sap density and therefore hardiness, in peach trees, cabbage 

 and tobacco plants, by heavy applications of potash fertihzers were 

 not successful in attaining either object. ^^ European writers have 

 claimed increased hardiness from phosphate or potash applications; 

 their evidence, however, is not entirely convincing. 



Wilted tissue, presenting another case of increased sap density through 

 withdrawal of water, was tested for hardiness by Chandler with no 

 significant results. This seems entirely consistent since the sap density 

 in this case is the result, not of the addition of substances in solution, but 

 rather of the withdrawal of water and may be closely comparable to the 

 initial stage of freezing itself. When a longer and slower wilting appeared 

 to be induced on dormant peach twigs, possibly resulting in a somewhat 

 more fundamental change in the protoplasm, hardiness seemed increased. 



By Increasing Water-retaining Capacity. — Another consequence of 

 the theory that death is due to the withdrawal of water from the cell 

 and later from the tissue, is that resistance to cold must be increased by 

 factors tending to increase the water-retaining capacity of the cells. 



Observations on the moisture content of apple twigs reported by 

 Beach and Allen, ^^ shown in Table 13, reveal an important relation to 

 hardiness. From July to December there is considerable variation in the 

 moisture content of the several varieties. On Jan. 15, however, following 

 several days of severe cold, the two hardiest varieties. Hibernal and 

 Wealthy, have a noticeably higher moisture content than the tenderer 

 varieties; furthermore, the loss of water from July to January is very 

 much less in these two hardiest varieties than in the others. 



Data of similar purport, drawn on for Table 12, are reported by 

 Strausbaugh^^^ in Minnesota. Water losses accompanying markedly 

 cold weather were greater in the less hardy plums. Following a period of 

 relatively warm weather the less hardy varieties showed a marked 

 increase in moisture content, possibly because they were less dormant, 

 possibly because they had lost more. 



These observations indicate that the actual moisture content of a 

 tissue at most times has less connection with hardiness than its water- 

 retaining capacity. The water lost is less significant than the water 

 retained. Protection against injury from low temperatures depends on 

 the amount of water the plant can retain at a critical moment against the 

 great force which tends to draw water out of the cells to form ice crystals 

 in the intercellular spaces. This force can be appreciated by the familiar 

 ability of growing ice crystals to split rocks. To hold water against this 

 influence, the protoplasm must have a certain amount of its moisture 

 supply in a form which is not easily frozen. In the section on Water 

 Relations plant tissue is shown to contain, in addition to its free and readily 

 frozen water, water in an adsorbed or colloidal state, which does not 



