FORMATION OF FROST RINGS IN CONIFERS. 13 



Hartig (#, p. 7) likewise mentions the occurrence of chains of 

 abnormal resin canals, which he regards as due to the action of late 

 frost, throughout the entire circumference of the phloem of stems of 

 Chamaecyparis lawsoniana 2 centimeters thick, at a slight distance 

 from the cambial layer. He states that these arise by the medullary 

 rays stretching and becoming broadened laterally through cell divi- 

 sion and that between each two rays the delicate-walled tissue com- 

 posed of sieve tubes and parenchyma was crowded apart. He as- 

 sumes that here also the tissue gaps are not closed after the thawing 

 of the ice, and finds that the surrounding living cells become en- 

 larged more or less into these gaps and become converted into resin- 

 secreting cells, pouring large quantities of resin into them. As a 

 result of this formation a festoon of large resin beads appears from 

 the bark on the ends of cut-off shoots. The writer, however, did 

 not observe any formation of chains of pathologic resin canals in 

 the phloem of the frost-injured materia^ of Chamaecyparis law- 

 soniana studied by him. 



SUMMARY. 



The pathological anatomy of late- frost injury has been studied in 

 detail by the writer in Pinus albicaulis, P. contorta, P. densiflora, P. 

 lambertiana, P. monticola, P. ponderosa, Picea engelmanni, Larix 

 occidentalism Pseudotsuga taxi folia, Abies grandis, A. lasiocarpa, 

 Tsuga heterophylla, T. mertensiana, Thuja plicata, Chamaecyparis 

 lawsoniana, Sequoia w ashing toniana, and Taxus baccata; also in 

 apple and pear trees. 



The young shoots injured by late frost may either wilt through 

 loss of turgor and after again directing their points upward usually 

 become permanently distorted, or, as generally happens, they may be 

 killed outright and replaced by one or more volunteer shoots. The 

 structural disturbance initiated by the action of late- frost injury is 

 not confined to the shoots then developing, but extends down the 

 stem for distances varying from several inches to several feet below 

 the base of the injured shoots, or as far as the cambium has been in- 

 jured by the freezing without entailing the death of the stem. The 

 healing proceeds internally and results in the formation of a brown- 

 ish zone of parenchyma wood, or frost ring, within the growth ring, 

 developing at the time of the injury. 



Late- frost injury results in very characteristic disturbances in the 

 tissue of the growth ring forming at the time of the injury. The 

 abnormal tissue of the frost ring varies greatly, according to the 

 severity of the injury, and may be characterized by various combi- 

 nations of such features as the crumpling of the wood cells that were 

 but slightly lignified at the time of the injury, a marked broadening 

 or proliferation of the medullary rays, a strong lateral displacement 

 of the medullary rays together with a marked broadening or pro- 

 liferation, the presence of radial clefts subsequently filled up by 

 large-celled parenchyma, and more or less broad zones of wound 

 parenchyma. The displacement of the medullary rays is occasioned 

 by their stretching and lack of elasticity ; the radial clefts, to the pre- 

 ponderance of the tangential contraction over the radial contraction ; 

 and the interpolated zone of parenchyma wood, to a transitory weak- 

 ening of the compressing influence exerted by the bark girdle on the 

 cambium, due to the disrupting action caused by the freezing. 



