Killing of Plant Tissue by Low Temperature 145 



13. Of the tissue above ground during periods when the most 

 complete maturity is reached, the most tender parts are the pith 

 cells and the fruit buds. During periods of rapid growth there is 

 little difference in hardiness of the different tissues. The tissue 

 which is most tender at all seasons of the year is the root. There 

 is much less difference, however, in the killing temperature of roots 

 in summer and winter than between the killing temperature of twigs 

 or other wood in summer and winter. (Pages 224-239). 



14. Roots of the French crab used as stock seem to be more 

 tender than roots which come from scions of an average variety of 

 apple (Pages 239-243). 



15. Marianna plum roots are certainly more hardy than Myro- 

 bolan roots, and Mahaleb cherry roots seem slightly more hardy than 

 Mazzard roots. (Pages 243-252). 



16. That part of the root system nearest the surface and the 

 largest, oldest roots are more resistant to cold than are small roots 

 further from the surface. (Pages 233-252). 



17. Pollen of the apple will withstand much lower temperatures 

 than will any other tissue of the flower when in full bloom. (Page 

 253). 



18. Scales of peach buds do not serve to protect them from low 

 temperature. Buds frozen in the laboratory with the scales removed 

 were slightly more resistant to low temperature than were buds with 

 the scales not removed. (Pages 254-256). 



19. The killing of wood of peach trees from freezing is one of 

 the most important determining factors in peach growing. Little 

 can be done to influence the amount of killing except to have the trees 

 start into winter in proper condition of maturity. The weakest 

 growing trees, however, do not generally reach this condition of ma- 

 turity in the most satisfactory manner. Trees one or two years in 

 the orchard, or old weak trees, are most liable to succumb to effects 

 of low temperature. Pruning the trees severely following a winter 

 when the wood has been killed, altho apparently in the best condition 

 of maturity, seems to reduce the amount of killing. However, such 

 pruning following winters when the wood has been killed on account 

 of its not having reached the proper condition of maturity in the fall, 

 generally due to the presence of wet weather following a drought the 

 season before, is liable to result in greater loss than if no pruning 

 were done. (Pages 256-266). 



20. The hardiness of peach buds when in fully dormant condi- 

 tion seems to be greatly increased by continuous low temperature 

 preceding the date at which the temperature goes low enough to kill. 

 This capacity to withstand hnv Icuipcratures seems likely to bi' due 



