INJURIES DUE TO ATMOSPHERIC INFLUENCES 293 



wood-ring are still in an embryonic condition and with their 

 walls unlignified, and the plastic substances have not yet been 

 converted into reserve materials. Such trees display the same 

 sensitiveness to winter frost that our indigenous trees do to 

 late spring frost. After a rapid thaw the interrupted chemical 

 processes induce decomposition. 



Numerous pathological phenomena in plants have been 

 erroneously attributed to frost, and in particular so-called tree- 

 canker has frequently been ascribed to this cause.* Most of the 

 forms of canker are infectious diseases, and it is only in a few 

 extremely frosty localities that I have had 

 the opportunity of noticing cancerous spots 

 which were undoubtedly due to frost. These 

 were met with on a great variety of dicoty- 

 ledonous trees, and in order to distinguish 

 this form of disease from the work of can- 

 ker-inducing fungi I have designated it 

 " Frost-canker." 1 



Frost-canker always occurs at the base 

 of a lateral branch that has been killed 

 by severe late frost. The first symptoms 

 are found in the callus which surrounds 

 the base of the dead branch. Should the 

 locality (frost-hollow) be visited by late 

 frosts during a scries of years, the callus, 

 which has not had time to protect itself 

 by a dense firm periderm, is killed in the 

 month of May by frosts which occur after 



the tissues have resumed the state of vegetative activity. The 

 tissues often die to the distance of half an inch or more from 

 the base of the branch (Fig. 158). Subsequently a new callus 

 forms under the dead and rapidly decomposing cortex. Should 

 the plant be unaffected by late frosts for several successive years, 

 these canker-spots may heal up completely. But, on the other 

 hand, should such frosts recur, the canker-spot increases in size 

 with each unfavourable year. The fact that frost-canker makes 



1 R. Hartig, Untersuchungen, I. p. 135, Table VII. 



*[See Sorauer, Pflanzenkrankheiten, B.I. 1886, for the arguments in 

 favour of this view. ED.] 



FIG. 158. The branch 

 of a beech showing 

 frost- canker in the 

 vicinity of the base of 

 a shoot that has been 

 killed by frost. The 

 wood is brown intern- 

 ally. Natural size. 



