WINTER INJURY TO THE ROOTS 305 



These seasonal differences obtain, not only in the apple seedlings, but in all the 

 roots reported in this paper." 



Another interesting factor in root injury is reported by Carrick, He finds 

 that, "the resistance is in direct proportion to the diameter of the root," and 

 suggests that this fact accounts for the occasional observation in laboratory 

 freezings of root killing at the tips when the roots near the crown are uninjured. 



A study of Table 38, with the killing temperatures given above in 

 mind, shows that the average soil temperatures in the recognized fruit 

 growing sections noted are substantially above the danger point and 

 suggests one reason why fruit growing in certain other sections requires 

 some special precautions. Attention is due, further, to the consideration 

 that these are average figures in which fluctuations to lower points are 

 submerged. In Table 40 the actual seasonal minimum temperatures at 

 one point are segregated. It is particularly significant that the winter of 

 1898-1899, when the soil temperature at Lincoln, Neb., reached 7°r., was 

 the winter characterized by an extreme amount of root killing in lowa,^"^ 

 Wisconsin^'' and Ontario."^ 



Factors Influencing Frost Penetration. — Temperature alone, or air 

 temperature alone certainly, is not the sole controlling factor in root 

 killing. A temperature of — 20°F. maintained for several days has 

 caused extensive root killing in Ontario.^" Goff" in an interesting survey 

 of an extensive area involved in the freeze of February, 1899, found little 

 damage in several regions where the unofficial temperatures went as low 

 as — 50° or even — 52°F., though in no case where root killing occurred 

 had the temperature gone below — 36°F. A report from Waukee, Iowa, 

 indicated root killing with a minimum of — 24*'F. ; other localities suffered 

 severely at — 23°F. 



Protection Afforded by Snow. — The principal difference lay in the 

 fact that in some sections snow lay on the ground while in others there 

 was none. Goff's analysis showed 34 localities with more or less snow 

 at the time of the freeze; of these, 20 reported definitely that the chief 

 injury was in the tops, three reported roots and tops equally damaged, 

 while in one there was more injury to roots than to tops in apples but 

 more in the tops of cherries and plums than in the roots. Fifty-seven 

 localities were without snow at the time of the freeze; definite statements 

 of comparative injury indicated 43 cases where the principal damage was 

 in the roots, 3 placed it in the tops and 1 reported roots and tops 

 equally damaged. 



Similar testimonials concerning the value of a snow covering are 

 common in pomological literature. Quantitative data applicable here 

 are given by Bouyoucos." Table 42, arranged from his figures taken at a 

 depth of 3 inches, shows the temperature differences between ground 

 without snow, ground under compacted snow, under uncompacted snow 

 and under vegetation plus compacted snow. 



