Jan. 1923] annual report 7 



injury of 31.5%, and those exposed for 18 hours showed an injury of 43.5%. 

 Thus a gradual increase in the amount of injury is by no means propor- 

 tional to the increase in the length of time of exposure. 



A series of nine lots of roots were partially dried by exposing to the at- 

 mosphere of a storage cellar for 24 hours previous to the freezing test. When 

 exposed to a temperature of minus 7.8° centigrade for one-half hour after 

 a gradual fall, these roots showed an injury of only 12.8% or about one-half 

 the injury which normal turgid roots receive under the same conditions. 



A fourth series of roots was very suddenly frozen, the temperature being 

 dropped to a minimum of minus 7.8° in about 30 minutes instead of six 

 hours. These roots showed very much increased injury over those frozen 

 under a gradual fall of temperature. 



Tests were also made of the relative injury to roots frozen in dry sand, 

 in saturated sand, and medium moist sand. The imlividual lots varied 

 widely under these conditions. In the saturated sand, iov instance, one 

 lot showed an injury of 45%, while another showed an injury of 70.5%. 

 It is evidently impossible to control the fall of temperature and other con- 

 ditions in wet or moist sand sufficiently to get uniform results. The average 

 injury for the series was greatest in the wet sand, and was greater in the 

 moist sand than in the dry. This agreed with previous results although 

 it must be remembered that the average is not accurate when so much in- 

 dividual variation occurs in different lots. 



Another line of work under the winter injvuy project was a study of the 

 structure of individual roots which had proved hai-dy in the tests of 1921 as 

 compared to roots which had proved very tender in these same tests. Por- 

 tions of the roots which had been placed in killing solution in 1921 at the time 

 when the tests were conducted were embedded in celloidin, and microscope 

 slides were prepared. A study was also made of one or two roots which . 

 had shown slight injury. The sections of roots showing injury indicate 

 that the most tender tissue of the roots is the immature xylem. Cells of this 

 region were killed and discolored when the other cells of the root were en- 

 tirely uninjured. It was thought that the more hardy roots may be those 

 which are best matured in autumn, and that the degree of maturity might 

 be indicated by the number of actively dividing cells in the cambium layer 

 and by the number of immature xylem and phloem on either side of the cam- 

 bium. A considerable number of sections were prepared from each of 12 

 roots, but a study showed that there is no correlation between the number 

 of immatiu-e xylem and phloem cells, and the resistance of the root to low 

 temperature. No structural characteristics were found which would be 

 associated with either hardiness or tenderness. 



The results secured to date indicate that the environmental conditions 

 during freezing such as length of exposure to cold temperature, the rate of 

 temperature fall within limits which are possible under field conditions and 

 the rate of thawing after freezing are of relatively small importance; the 

 amount of injury depends most largely upon the degree of temperature to 

 which the roots are subjected. 



