BODY AND BRANCH DISEASES AND INJURIES 49 



higher temperature than if the rate of fall was more gradual ; 

 (4) the tensions set up in the bark and wood by the alternate 

 increase and decrease of the temperature cause mechanical 

 separation of the bark from the wood and this destroys the 

 cambium region. The cankered areas commonly found at the 

 base of the trunk are explained in the same way. Various 

 species of saprophytic and semi-saprophytic fungi soon appear 

 and produce their fruiting-bodies on the dead bark. The 

 repeated attempts at callusing on the edge of the canker may 

 fail, because the callus tissue, being largely parenchymatous, 

 is susceptible to freezing-injiu-y and is killed. 



To prevent woimd parasites from gaining a foothold and 

 causing further damage to the tree, surgical methods should 

 be used and the wound protected. For the proper procedure 

 in removing the dead bark and shaping the wound, see page 

 351. As a dressing for such wounds it would be advisable to 

 use pure white lead paint, renewing the dressing at least once 

 every year. By using a white dressing instead of a black one, 

 some added protection is afforded the callusing edges of the 

 wound, since the sun's rays will not heat the bark to as high 

 temperature. 



References 



Mix, A. J. Sun-scald of fruit trees, a type of winter injury. Cornell 



Univ. Agr. Exp. Sta. Bui. 382 : 235-284, pis. 18 and 19, figs. 60 



and 61. 1916. 

 Chandler, W. H. The killing of plant tissue by low temperature. 



Missouri Agr. Exp. Sta. Research Bui. 8 : 141-309. 1913. 

 Hartig, R. The action of frost. In Text-book of the diseases of 



trees, pp. 282-294, figs. 157-158. 1894. 

 Zon, R. O. Effect of frosts upon forest vegetation. Forest Quarterly 



2 : 14-21. 1903. 

 Stone, G. E. Winter-kiUing. Massachusetts Agr. Exp. Sta. Ann. 



Rept. 18:228-233. 1906. 

 Stone, G. E. Frost cracks, winterkilling of cork cambium and sun 



scald. In Shade trees, characteristics, adaptation, diseases and 



care. Massachusetts Agr. Exp. Sta. Bui. 170 : 204r-208, figs. 



77-80. 1916. 



