28 



Depressions were not determined for each day's freezing on 

 account of the limited number of plants, but depressions taken of 

 other lots grown under the same conditions show similar results. 

 Thus a set taken January 6, 1912, showed the following depressions: 

 Plants grown out of doors, depression, 1.470; plants grown in the 

 greenhouse with limited water supply, depression, 1.035; plants 

 grown in the greenhouse with abundant water supply, depression, 

 .990. Here again increased sap density is accompanied by greater 

 hardiness, and in this case the plants with the greatest density are 

 also the ones which grew most rapidly. 



In all of these cases any treatments that increased the density 

 of the sap lowered the killing temperature. It should be said, how- 

 ever, that in most cases where the density of the sap has been in- 

 creased, the growth of the plants has been checked so we can not say 

 positively that a treatment has increased the hardiness, due to the 

 density of the sap, since it could probably be due to the smaller cells 

 or some other differences in the conditions of the protoplasm. How- 

 ever, cabbage and kale were exceptions to this and actually grew 

 more rapidly out of doors and yet had more dense sap and were more 

 hardy. In order to test the effect of increased sap density on hardi- 

 ness under conditions where this effect on growth would be elimi- 

 nated, plants of tomato, cabbage, lettuce, kale and cowpeas were 

 grown under like conditions. Then the plants were pulled, the roots 

 washed clean and placed in sugar solutions and in potassium chlo- 

 ride and other solutions of varying strengths as shown in the table, 

 with the results to be seen in the following table. 



