Jan. 1922] annual report. 15 



fold: (1) to determine what tissues are injured by cold, and the diEferences 

 ia structure and composition between hardy and tender tissues; (2) to 

 determine what environmental conditions during the freezing and thawing 

 process influence the degree of injury; (3) to determine what conditions 

 of growth and nutrition tend to produce hardy tissues; (4) to test the feasi- 

 bility of developing a hereditarily hardy strain of root stocks which may be 

 propagated vegetatively. 



Approximately two thousand seedling apple roots were frozen last year 

 in tests designed to study the effect of freezing imder different conditions. 

 The data obtained does not wholly agree with that previously obtained in 

 similar experiments. The roots were subjected xmder varying conditions 

 to a critical cold temperature of about — 7.8° C. Immediately after freez- 

 ing they were planted in soil in the greenhouse and allowed to grow for from 

 sixty to ninety days. Observations were then made on the proportion 

 killed or injured. 



In the case of nine duphcate lots of roots the temperature was regulated 

 to fall slowly from freezing to the minimum and they were remo'^^ed one 

 half hour after the minimum was reached. In comparison another series 

 was held four hours and one series eighteen hours at the miminum. The 

 two last series were found to be injured shghtly more than the first, but the 

 difference was not great considering the accuracy with which it is possible 

 to determine the amount of injiu-y. Previous experience had indicated 

 that there was practically no difference between lots exposed to the same 

 minimum temperatm-e for long or short periods. 



One series of seven lots was frozen as rapidly as possible instead of at the 

 usual slow rate. A markedly greater injury resulted, although in previous 

 experiments little difference had been noted. 



A series of tests each respectively in dry, medium wet and very wet sand 

 showed gi-eatest injury in the wet sand. 



A series in which the roots were air dried for 24 hours previous to freez- 

 ing showed less injury from cold than normal turgid roots, but the drying 

 in itself killed many roots, as was evidenced by the dying of many of the dry 

 check roots which were not frozen. 



To gather further data on the relative hardiness of cion roots from different 

 varieties of trees, ten trees each of Hibernal, Duchess, Dudley and North- 

 western, which had thrown out roots above the union with the stock were 

 secured. These cion roots together with stock roots from the same trees 

 were subjected to a critical freezing temperature. Duchess and Hibernal 

 proved most hardy, Dudley next and Northwestern least hardy, results 

 which accord with previous experience. 



In freezing seedling roots some individuals prove much more hardy in 

 the same test than others. 



To determine whether this difference is related to the differences in size 

 of the roots, 300 roots which had been measured were frozen and a correlation 

 table constructed. It was showm emphatically that the injmy is not pro- 

 portional to the diameter of the seedling, the coefficient of correlation being 

 — 0.04 plus or minus 0.04. 



