12 UNIV. OF N. H. AGR. EXPERIMENT STATION [Bulletin 216 



Winter Injury Project. 



The experiments on relation of conditions of freezing to injury sustained by 

 seedling roots of the apple have been brought to completion by G. F. Potter 

 (Horticulture) and the results published as Technical Bulletin No. 27 of this 

 Station. 



Two lines of further work are in progress. The feasibility of propagating the 

 commercial varieties of this section upon a more hardy root stock is being 

 tested. A number of trees are now growing in the nursery which have been 

 propagated upon the Hibernal stock. This stock was found most resistant to 

 cold of all those which were tested, being approached only by the Duchess. 

 No tests of the possibility of using Duchess as a stock root are being carried on, 

 because results secured at the Massachusetts Station indicate that Duchess 

 does not make a suitable root system upon which to work other varieties. The 

 Hibernal root is not only hardy but vigorous, and if compatible with such 

 varieties as Baldwin, Mcintosh, and Wagener, it may prove enough better than 

 seedling stocks to warrant the expense of its use in propagation. 



Another phase of the work on this project consists of the detailed study of the 

 nature of the injury which results from exposure of the roots to low tempera- 

 ture. A considerable number of microscopic slides have been made showing 

 the development of roots after they are injm-ed by frost. The study of these 

 slides up to date indicates simply that, whereas in the normal root the rows of 

 cells in the meristimatic region are perfectly uniform and regular, roots which 

 have been allowed to start growth after being frozen show these cells to be 

 much distorted and arranged in irregular groups. In order to study the process 

 which brings about this arrangement of the cells, a number of roots were 

 subjected to low temperature and .samples preserved in kilUng fluid. 



Three lots of roots were frozen to provide material for sampling. One lot 

 was subjected to a medium low temperature such that it was expected that some 

 of the roots would not be injured and that others would show shght injury. A 

 second lot was subjected to the same temperature, but the i-ate of temperature 

 fall was made much more rapid so that it was expected that the injury would be 

 more severe and a certain proportion of the roots would be killed outright. A 

 third lot of roots was subjected to a rather low temperature at the usual rate of 

 temperature fall so that it was expected that severe injury would take place. 

 The samples preserved were marked as to the individual root from which they 

 came and include the cortex, cambium, and a small amount of the xylem in 

 each instance. Samples were taken 24 hours after the roots had been frozen, 

 again after three days, at the end of one week and at the end of two weeks. 

 Records of the final stage of injury reached by each root were made. A con- 

 siderable number of sections have thus been taken and only a beginning has 

 been made on the cutting, mounting, and staining of this material. It is 

 expected that the series will show the various stages of development of the 

 inj ury in the tissues. A considerable number of the roots were completely killed 

 by the freezing, and the slides from these roots should show the appearance of 

 this tissue after the freezing and before disintegration had actually taken place. 

 Work is also being undertaken to determine if possible the chemical difference 

 between the tender and hardy individuals of a random sample of seedhng roots. 



