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



5. In the experiments described in this bulletin, the killing 

 temperature of plant tissue that kills at relatively high temperature 

 has been reduced whenever the sap density of the tissue has been 

 increased. (Pages 155-187). 



6. In addition to ripe apples and pears, and the leaves of Agave 

 Americana observed by Miiller-Thurgau and Molisch, leaves of let- 

 tuce kill at a slightly lower temperature if they are thawed slowly 

 than if thawed rapidly. In case of all other tissues tested by this 

 station or by others, including unripe apples and pears, there is no 

 indication that the rate of thawing has anything to go with the 

 amount of killing at a given temperature. (Pages 187-l'94). 



7. Rapid wilting of tissue has not generally increased the re- 

 sistance of plants to low temperature over that of unwilted tissue 

 with a dry surface. However, tissue with a wet surface killed worse 

 at a given temperature than did tissue with no moisture on the sur- 

 face. (Pages 194-198). 



8. Slow wilting or partial withholding of water through a long 

 period increased the resistance of tissue to low temperature. (Pages 

 198-199). 



9. In case of hardy winter buds and wood, a rapid decline in 

 temperature greatly increased the severity of injury from a given low 

 temperature. (Pages 199-218). 



10. There seems to be no constant relation between the rate 

 of growth of plant tissue and resistance to low temperature. Young 

 leaves of fruit trees kill at a higher temperature than do old, mature 

 leaves, while the young leaves of lettuce withstand a lower tempera- 

 ture than do the older leaves. (Pages 218-222). 



11. Previous exposure to low temperature above that at which 

 the tissue kills seems to increase the resistance of tissue to low tem- 

 perature. (Pages 223-224). 



12. The most important feature afTecting the hardiness of 

 plant tissue is maturity, that is, the condition of resistance that 

 the plants reach during the winter dormant period. Maturity in the 

 case of cambium may be intimately associated with the process of 

 drying out. However, this can not be true at least of cortex of win- 

 ter twigs. There is little difference between the moisture content 

 of unfrozen cortex in seasons when it is very tender and seasons 

 when it is hardy. The wood at the base of the trunk and at the 

 crotches of all rapidly growing branches seems to reach a condition 

 of maturity in early winter more slowly than does most other tissue. 

 (Page 224). 



