258 POMOLOGY 



propos9d to account for crotch injury, such as drying out, 

 occurrences of ice at these points, and immaturity of the 

 wood. The latter, according to Chandler,^ is the principal 

 if not the only factor involved. The last tissue formed and 

 hence the most tender is near the base of the branches 

 (crotches) and near the bottom of the trunk of the tree. 

 This tissue becomes more hardy or mature as the season 

 advances. Hence, if veiy low temperatures occur early in 

 the winter, this tissue is the first that is injured. If the pre- 

 vious growing season is short and the tree as a whole goes into 

 winter in an innnature condition, the damage is enhanced. 



226. Collar-rot or injury is an affection of fruit-trees 

 localized at the crown or "collar." The injury may extend 

 down on to the larger roots and also some distance up the 

 trunk and it frequently encircles the base of the tree, result- 

 ing in its death. Such varieties of apple as the Grimes, Grav- 

 enstein, and King are particularly susceptible and for this 

 reason they are often top-worked on to resistant sorts. The 

 cause has been variously attributed to arsenical poison- 

 ing,2 parasitic organisms, and to freezing. 



Grossenbacher has shown that the primaiy injury takes 

 place in the winter in connection with severe freezing 

 weather and hence that fungi are not the chief cause but are 

 the agencies of decay following the winter injury. Chandler 

 has also pointed out that blight {Bacillus amylovorus) is not 

 the cause of collar-rot since the result of "body bUght" is 

 a tightening of the bark when it dies, which is the opposite 

 phenomenon of true collar-rot. The latter also holds that 

 collar-rot is doubtless due to direct freezing to death from 

 the low temperature and frequently to a rapid lowering of 



1 Chandler, W. H. Mo. Agr. Exp. Sta. Res. Bull. 8. 1913. 



2 Headden, W. P. Colo. Agr. Exp. Sta. Bull. 131. 1908. Grossen- 

 bacher, J. G. N. Y. (Geneva) Exp. Sta. Tech. Bull. 12 and 23. 1909 

 and 1912. 



