12 BULLETIN 1131, TJ. S. DEPARTMENT OF AGRICULTURE. 



In general, it appears that frost injury occurring shortly after the 

 initiation of active growth causes a greater distortion of the wood 

 elements than that occurring when the growth ring is practically 

 mature or when the tree is dormant. 



Frost rings are often confusing to those who have occasion to 

 engage in age determinations or stem analyses of trees. The frost- 

 ring formation, however, usually occurs within such close limits of 

 the beginning of the annual ring formation that, macroscopically at 

 least, the parenchyma zone appears to coincide more or less closely 

 with the outer limit of the preceding growth ring. Frost -ring 

 formation should prove confusing in age counts only when it occurs 

 late in the season after a considerable portion of the growth ring 

 has been formed. Moreover, since only the younger stems appear 

 to be susceptible to frost-ring formation, it is believed that in coni- 

 fers at least, false ring formation from this source need be expected 

 chiefly only in the first several growth rings formed in the life of 

 the tree. 



As may be expected from their structure, frost rings constitute 

 a plane of weakness in the wood, since there is no strong bond be- 

 tween the wood formed before the injury and the parenchyma wood 

 formed immediately after it. In chopping off a face on stems con- 

 taining one or more frost rings in order to follow their linear 

 extent, the wood frequently splits peripherally along the plane of 

 these zones of abnormal wood. In future years it seems likely, as 

 Somerville (11) states for the abnormality which he describes, that 

 they may lead to the formation of ring shakes within the trees. 



The writer's investigation of the pathological anatomy of late- 

 frost injury confirms those of Mayr, Hartig, and Sorauer in all par- 

 ticulars except the occurrence of the chains of pathologic resin 

 canals, which Mayr (4) suggests may be caused by frost and which 

 Hartig (2) found sometimes associated with the frost rings. 



Mayr (^, p. 29), in a discussion of the chains of abnormal or 

 pathologic resin canals sometimes found in the wood of Abies flrma 

 and Tsuga, suggests that they may be caused by late frost, which, he 

 states, is of fairly common occurrence. However, he observed that 

 such chains of resin canals may also be found in the hard summer- 

 wood zone of the annual ring, where late frost is excluded as a 

 cause. Although not considered by Mayr, a number of other types 

 of injury could easily have been responsible for this pathologic 

 resin-canal formation. 



Hartig (£, p. 7) states that he has repeatedly found that the wound 

 parenchyma developing in the frost ring contained resin canals, so 

 that a more or less complete ring of them was recognizable in the 

 frost zone. Despite the writer's particular consideration of this 

 point and his extensive investigations on pathologic resin-canal 

 formation in general, which will appear shortly, he has never ob- 

 served the formation of chains of pathologic resin canals as the 

 result of frost injury. While zones of pathologic resin canals do 

 occasionally coincide with the frost rings in a stem, the writer has 

 always traced their origin to some mechanical wound. It is by no 

 means impossible, however, for such zones of pathologic resin canals 

 to arise schizogenously within the broad aggregates of parenchyma 

 wood comprising the frost ring. 



