WINTER INJURY 259 



the temperature, and not to a tearing of the tissue or drying 

 out as described by Grossenbacher. 



That excessive alkali soils and arsenical poisoning are pri- 

 mary factors in collar-rot has also been generally abandoned 

 through the work of Headden ^ and Ball " in the first case and 

 Ball ^ and his associates in the second. 



The view was held by Headden that large quantities of 

 arsenic were found in trees suffering from collar-rot, but the 

 fact that normal trees also often contained fairly large quan- 

 tities of arsenic, that collar-rot occurred in orchards which 

 had never been sprayed, and that herbaceous plants were 

 growing about crown-rotted trees, caused this view to be 

 abandoned for the one of freezing. 



227. Frost-cracks or the splitting of bark or trunks of 

 trees often accompanies other forms of winter injuiy. 

 These cracks may extend up the entire length of the trunk 

 and follow up one or more of the main branches for some 

 distance, or they may be only a few inches in length. They 

 may open as much as two centimeters or may be merely 

 visible lines, but in any event they will draw together or 

 clos(» after the severe weather is over. 



228. " Black heart " is a common result of low tempera- 

 tures and consists in the killing of the sap-wood and pith, 

 although the cambium remains alive. As a result, the tree 

 continues growth and rapidly forms a new layer of sap-wood 

 within and bark without. Nursery trees are frequently 

 "black hearted," particularly pears, and they may make a 



Note :— Following the winter of 1917-18 the author inspected several 

 orchards of Ben Davis trees in the state of Maine in which the damage 

 took the form of crotch injury almost entirely and while the trees were 

 partly alive they were entirely beyond hope of repair. 



1 Headden, W. P. Colo. Agr. Exp. Sta. Bull. 157. 1910. 



2Ball, E. D. Jour. Econ. Ent. 2: 142-48. 1909. 



3 Ball, E. D. el al. Jour. Econ. Ent. 3: 187-97. 1910. 



