﻿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 

 [•ays stretching and becoming broadened laterally through cell divi- 

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

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

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

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

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

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

 'esult of this formation a festoon of large resin beads appears from 

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

 lot observe any formation of chains of pathologic resin canals in 

 lie phloem of the frost-injured material of Chamaecyparis law- 

 loniana studied by him. 



SUMMARY. 



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

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

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

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

 Vsuga heterophylla, T. mertensiana, Thuja plicata, Chamaecyparis 

 awsoniana, Sequoia washingtoniana, and Taxus baccata; also in 

 ipple and pear trees. 



The young shoots injured by late frost may either wilt through 

 oss of turgor and after again directing their points upward usually 

 )ecome permanently distorted, or, as generally happens, they may be 

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

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

 lot confined to the shoots then developing, but extends down the 

 item for distances varying from several inches to several feet below 

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

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

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

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

 leveloping at the time of the injury. 



Late-frost injury results in very characteristic disturbances in the 

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

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

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

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

 >ut slightly lignified at the time of the injury, a marked broadening 

 >r proliferation of the medullary rays, a strong lateral displacement 

 >f the medullary rays together with a marked broadening or pro- 

 iferation, the presence of radial clefts subsequently filled up by 

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

 >arenchyma. The displacement of the medullary rays is occasioned 

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

 ponderance of the tangential contraction over the radial contraction ; 

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

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

 ;ambium, due to the disrupting action caused by the freezing. 



