!N"eW York ArfRTOTTLTITRA-L ExPE1?TMElvrT SrATTOTir, 305 



side of trees and on trees so situated that the sun rarely shines on 

 their trunks the " sun-scald " hypothesis appears untenable, while 

 the wind swaying and excessive evaporation theory of Bernbeck 

 seemsto afford an explanation of the observed facts. As stated before, 

 more or less thickly scattered groups of cells in the inner phloem and 

 inner cortex are injured first and sometimes all around a trunk or an 

 ascending branch, but in severe cases the interspersed living groups 

 also die; first on the windward side, and in extreme cases the entire 

 bark subsequently dies on upright shoots. Such shoots are then said 

 to have been " winter-killed." In the " sun-scald " and " winter- 

 killed " types of injuries the bark does not sustain radial clefts but 

 is frequently wind-checked after it dies. In case the initial injury 

 in the phloem and inner cortex has not been severe enough to result 

 in the typical " sun-scald " effect the bark on the windward side of 

 trunks frequently dies only in patches during the summer, as is shown 

 in figure C on Plate XVIII. 



The injuries of last winter which included radial clefts, usually also 

 involved the wood cylinder. In many of these cases the bark was 

 not loosened. In considering the contraction of tree trunks (page 36) 

 occurring during the time of injury it seems likely that the clefts, 

 especially in cases where the bark had not been loosened, were mainly 

 due to low-temperature contraction in the wood. Yet it appears 

 probable that v/ind swaying was also concerned in the production of 

 wood clefts which extended through the entire wood cylinder like those 

 shown on Plates XX and XXIX, because it is inconceivable how 

 tensions due simply to peripheral contraction could result in wood 

 clefts extending far beyond the pith. In instances like the one shown 

 on Plates XXVIII and XIX, where there was a combination of bark 

 loosening and radial clefts iii both wood and bark, the bark tension 

 must have been high on the approach of winter. It would appear, 

 then, that the chief difference between the winter injuries of the past 

 two years involving radial clefts, is their occurrence at different tem- 

 peratures. In the winter of 1910-11 the injuries occurred during only 

 moderately low temperature and the bark alone was cleft; while last 

 winter the temperature was very low during the time of their occur- 

 rence, and resulted in wood clefts also. In many cases of last winter 

 the bark loosening did not accompany the clefts, presumably because 

 the tension in the bark was but little in excess of that in the wood. 

 But the wind was probably a factor in both cases. 



Low temperature probably caused the bark injuries in crotches of 

 young apple trees by increasing the bark tension due to growth. The 

 wind seems to have had only a secondary influence in those cases 

 since no clefts resulted. Nordlinger attributed crotch injuries to 

 early cold weather and the immature condition of the tissues at such 

 points. 



The relation of growth and low-temperature tensions and the 

 strain induced by high winds, to the initial injuries resulting in rots 



