569 



changes in their radial course in the older annual rings, than in the younger 

 ones, or by the radial si)]itting of one or two annual rings in the wood disc. 

 Such inner clefts then have the form of a lance tip. i. e., are l)roadened at 

 the centre. Since in clefts extending to the hark the wound remains open, 

 the circumvallation walls incline toward the cleft and, therefore, form no 

 projecting ridges in frost clefts. 



Fig. 123. Oak stem cleft li\ Polyporiis sulfureus. (After Frank- Schwarz.) 



Frost Blisters. 



In connection with frost clefts, the so-called "internal frost tears" 

 should Vie considered, which R. Ilartig' has observed in oaks and firs. 



"If the tree shrinks with great cold"- he says, "tears can arise in the 

 wood body on the surface of the cleft which, however, extend only to the 

 bark mantel zvithout splitting it. The bark, which has no radial cleft sur- 

 faces, holds the wood body together. However, the elastic bark of the nr 



1 Hartig-, R., Innere Frostspalten. Forstl-naturwis; 



2 Lehrbueh der Pflanzenkrankheiten, 1900, p. 214. 



Zeitschr. 1896, p. 483. 



