FORMATION OF FROST RINGS IN CONIFERS. 3 



Petersen (9) describes and illustrates the zone of parenchyma 

 tissue or frost ring which resulted in a double-ring formation in 

 beech trees which had suffered from frost on May 17 and 18 in 

 Holland. 



Tubeuf (i^- pi. 31, fig. 1), in an article upon the pathological 

 anatomy of spruce trees that were dying back from the top in 

 consequence of drought injury, evidently for the sake of compari- 

 son, illustrates a portion of a frost ring in a small tree of Picea 

 excelsa. However, he makes no allusion in the text to frost injury, 

 which would seem to be due to his apparent failure to publish the 

 concluding part of the article. 



Sorauer, who was able to add the action of frost to the causes 

 which bring about the formation of false annual rings (12, p. 320), 

 later gives the details of an extensive study to determine the effects 

 of early and late frosts on the mature and immature wood of a 

 large number of fruit and forest trees (13). He found that erup- 

 tions in the vascular cylinder are generally manifested either in 

 radial clefts within the medullary rays or in tangential cracks 

 within the cambial region. In addition, many cavities appear in 

 the pith and the bark parenchyma. The separated tissue within 

 the cambium region gradually heals over, after presenting the ap- 

 pearance of a ring growth of two years. Sorauer discusses the for- 

 mation of double rings from the activity of frost and gives the 

 same account of this in the last edition of his manual of plant 

 diseases (12) as well as a detailed account of the injurious action of 

 frost injury in general upon plant tissue. Here (p. 577) he describes 

 the brown circular zones, or " frost lines," frequently occurring in 

 fruit trees after spring frosts and composed of collapsed, misshapen 

 cells. The occurrence of this phenomenon was also investigated 

 experimentally in artificial freezing experiments. 



Graebner (i), who investigated the action of late frosts on oak, 

 beech, spruce, and fir, makes no mention of frost-ring formation 

 as such, but does mention a wound-parenchyma formation that can 

 be followed back into the 2-year-old and 3-year-old wood. 



Neger (7) investigated a tip blight of Picea excelsa with which 

 two ascomycetous fungi were associated; however, they were found 

 only on snoots that had been injured by frost. Sections of the 

 stems, taken both through the dead tips and through the still living 

 stems, showed a more or less broad zone of parenchyma wood or 

 frost ring occurring in the beginning of the 1913 growth ring. 

 Since this parenchyma zone followed immediately upon the summer 

 wood of the 1912 growth ring and was not preceded by normal 

 spring- wood tracheids, it was assumed that a late frost was not in- 

 volved, but rather an early frost occurring in the fall of 1912. While 

 the frost of 1912 did not come particularly early, relatively low tem- 

 peratures occurred in comparison with other years, following upon 

 a cold wet summer, which greatly retarded the maturation of the 

 axial growth of that year. This injury therefore was considered to 

 be more nearly due to the action of the winter frost upon immature 

 wood. Tubeuf (15) had previously briefly described and illustrated 

 a tip blight of Picea excelsa due to the same causes, but he does 

 not go into the pathological anatomy of the injured shoots. Accord- 

 ing to Xeger, the frost injury had the effect of suspending or at least 



