176 Missouri Agr. Exp. Sta. Research Bulletin No. 8 



It seems then practically certain that one is justified in assum- 

 ing that the fruits in the above freezing table had their osmotic 

 strength increased as much by taking up the glycerine and sugar 

 solutions as this depression data indicates. The fruits that had 

 absorbed the glycerine were apparently fully turgid while the wilted 

 fruits were very flaccid. It is certain that wilting could have had 

 little part in increasing the sap density of the fruits absorbing the glyc- 

 erine. It may be suggested by some that possibly the tissue could 

 not absorb these rather strong solutions as rapidly as it could absorb 

 water, so there might be some wilting to cause the greater hardiness 

 attributed to the increased sap density. Observations were made on 

 this point in all cases and rarely was there any signs of wilting in the 

 frozen tissues referred to. In most cases, plants which were wilted 

 until they were very limp before treating as described above were 

 still less hardy than those absorbing the solutions. It is thus cer- 

 tain that the greater hardiness of the tissue absorbing the various 

 solutions was not due to wilting. The effect of wilting on tissue is 

 discussed later in this paper. 



Reducing Sap Density by Shading. The sap density of leaves 

 is known to increase from morning to afternoon. Leaves shaded 

 usually have a lower sap density than those in the light. It was 

 thought that this would be another good means of testing the effect 

 of sap density on hardiness. The following plants (or twigs contain- 

 ing leaves) were shaded for twenty-four hours and taken for freezing 

 in early afternoon along with plants under similar conditions, ex- 

 cept that they were in full sunlight. The results are shown in Table 

 10: 



Table 10. Showing Effect of Shading on Sap Density and 



Resistance to Freezing. 



Material 



Cowpeas 

 Cowpeas 

 Cowpeas 

 Cowpeas 

 Cowpeas 

 Cowpeas 



Treatment 



Shaded. . . . 

 Not shaded 

 Shaded. . . . 

 Not shaded 

 Shaded. . . . 



Date 



June 

 June 

 June 

 June 

 June 



14,'13 

 14,'13 

 14,'13 

 14,'13 

 17, '13 



Not shaded June 17, '13 



Per- 

 cent- 

 age 

 All 

 Killed 



Per- 

 cent- 

 age 

 Total 

 Leaf 

 Area 

 Killed 



0.0 



100.0 



0.0 



0.0 



66.6 



25.0 



90.0 

 100.0 

 90.0 

 22.0 

 66.6 

 81.2 



De- 

 pres- 

 sion 



.852 

 .980 

 .852 

 .980 

 .855 

 .947 



