6 N. H. AGR. EXPERIMENT STATION [Bulletin 208 



RESULTS OF WORK IN ADAMS PROJECTS. 



Winter Injury of Apple Roots. 



What happens when the roots of an apple tree are frozen, and what may 

 be done to prevent such a condition? In investigating this problem G. F. 

 Potter (Horticulture) has found several points of interest during the past 

 year. The results to date indicate that it is not feasible through soil manipu- 

 lation or cultural treatments to hope to reduce winter injury, except in so 

 far as the use of a mulch or cover crop may prevent penetration of frost into 

 the soil. On the other hand, different seedling roots have been found to 

 vary widely, in their resistance to cold, some being very tender and some 

 relatively hardy. While this difficulty cannot be overcome so long as seed- 

 ling roots are used for propagation of the apple tree, the tests have shown 

 that scion roots, especially those taken from the Hibernal and Duchess 

 varieties, are very much more hardy than the seedling stocks. A considerable 

 number of trees have been grown in the nursery under contlitions whicli 

 would tend to make them produce scion roots. This material was dug 

 in the fall of 1922, and will be used for experimental purposes during the 

 winter of 1922-23 and the season of 1923. The object of these tests will be 

 to further establish the relative hardiness of different varieties of scion roots, 

 and to test the feasibility of propagating named varieties upon vegetatively 

 propagated scion roots rather than upon seedling stocks. If it is commer- 

 cially possible to grow a tree upon a Duchess or Hibernal root stock, these 

 trees will be of great v^alue for planting in northern climates where more or 

 less insidious injury to the root system of the trees occurs almost annually. 



A discussion of the details of the experimental work may be helpfid in 

 showing the nature of this project. In the first place, the influence of the 

 conditions under which the roots are frozen upon the resulting injury was 

 studied in order to check results which had previously been obtained. All 

 the roots were subjected to a temperature of minus 7.8° centigrade. 



Before being frozen the seedling roots were stored at a temperature just 

 above freezing, and as soon as they had been exposed to the test they were 

 returned to storage under the same conditions. The injured tissues turned 

 dark in from four to eight weeks, but roots uninjured by the low tempera- 

 ture were preserved in perfect condition until the following spring. In 

 previous experiments the roots had been taken from cold storage and after 

 freezing placed in a warm room under growing conditions. The new method 

 of returning the roots to cold storage after exposure to low temperature 

 gives much more reliable results, as is indicated by perfect preservation 

 of the check roots which were not frozen. In one of the series the fall in 

 temperature was a gradual one occupying about six hours, and the roots 

 remained at a minimum temperature for one-half hour. In a second series 

 the fall in temperature was at the same rate as the first, but the roots 

 remained at the minimum temperature for a period of four hours; and in 

 still another series the roots remained at the minimum temperature for 

 eighteen hours. The average for nine separate tests showed that the roots 

 exposed to the minimum temperature for one-half hour received an injury 

 of about 27% while those exposed for an additional SJ^ hours received an 



