Killing of Plant Tissue by Low Temperature 241 



These roots were in all cases kept during the time preceding 

 the freezing in such a position that all parts must have been exposed 

 to practically the same temperature, so it is not possible that the 

 diminished hardiness of the parts furthest from the crown could 

 have been caused by their being exposed to a higher temperature 

 during the period preceding the freezing. It probably represents 

 the most rapidly growing tissue, but at times of freezing the tissue 

 had not been growing for at least three months. It also represents 

 tissue that under normal conditions is not so liable to be exposed 

 to low temperatures so in the evolution of the plant it would not be 

 so necessary for it to develop hardiness. 



Of great interest, practically, is the hardiness of various stocks 

 of fruit trees. Through the courtesy of Mr. E. S. Welch of Shenan- 

 doah, Iowa, this station was able to study various stocks. In the 

 case of apple trees worked on French crabs, a considerable number 

 of trees were furnished that had rooted from the scions, as well as 

 from the stock, thus permitting a comparison between these scion 

 roots and the roots from the stock. The trees were received Decem- 

 ber 20, 1912 and were heeled-in in the shade. The roots were thus at 

 a temperature near the freezing point from the time they were re- 

 ceived until they were frozen. The following table gives the results: 



