New Yoek Agricultural Expeeimext Station. 301 



Swaying is said to decrease transverse tension at the point of bend- 

 ing and is followed by an increase in the rate of growth at that region. 



Kraus also found many very small longitudinal clefts in the smooth 

 outer bark of Acer, ^sculus, and Salix, during winter and extending 

 as far as the cambium in some cases. The clefts are attributed to 

 transverse tension. 



From this work it appears highly probable that toward the end of 

 a vegetative season the bark tension on a tree which increased much 

 in diameter as compared with its former diameter, may be much 

 greater than on one having made but little growth. It is also apparent 

 that in case vegetative activities are inhibited prematurely in fall or 

 continued in full vigor abnormally late owing to uncommon environ- 

 mental conditions, the seasonal maximum bark tension may be re- 

 tained through the following winter. The bark on trees entering 

 the dormant season with high growth tension maxima at certain 

 regions of trunks and branches, is subject to excessive strains in the 

 high pressure areas when the temperature drops suddenly through 

 many degrees; that would be true regardless of whether the tempera- 

 ture sank low enough to be injurious to perennial plants or not. 



The above field observations show that the initial injuries resulting 

 in crown-rot and cankers usually occur at points which are in close 

 agreement with the location of the regions of maximal bark tension 

 found by Kraus, and in view of the researches of Sorauer which seem 

 to show that low temperature injury is often due to the tensions in- 

 duced rather than to the degree of cold, it appears probable that 

 initial injuries of this type are due to the combined effect of tensions 

 resulting from differences in growth rate, their increase by low tem- 

 perature, and the additional strain caused by bending in time of 

 strong winds. 



In the case of the experiment discussed on pages 32 and 44, the 

 temperature was probably too low to enable one to distinguish be- 

 tween the effect of the degree of cold and the tensions induced. It 

 seemed strange, however, that some bark was loosened on a tree on 

 which it had been slit; yet it does not show that the old notion of 

 slitting the bark on the trunks of rapidly growing trees is erroneous, 

 for it may be that if slit at certain times and allowed only time enough 

 to heal the wounds before the dormant period arrives some injuries 

 due to excessive bark tensions might be avoided. 



The wind as a factor in causing crown-rot. — As was often noted in 

 the field observations the relative wind exposure to which different 

 orchards are subjected seemed to make a decided difference in the 

 amount of winter-injury resulting. The injuries occurring on tree 

 trunks above ground and below the crotches were usually oriented 

 with reference to the prevailing wind. In case the location of the 

 injuries was not determined by the prevailing wind they were never- 

 theless on the sa7ne side in any particular orchard or locality, indi- 

 cating that the wind may have come from that direction during the 



