FORMATION OF FROST RINGS IN CONIFERS. 7 



directly from the base of the volunteer leader, at an elevation of 158 centi- 

 meters to an elevation of 30 centimeters above the ground. In these first three 

 trees there was no evidence of any frost injury in the growth rings of any year 

 other than those enumerated. 



Tree No. 4. — The original leader of this sapling had been killed, and a 2-year- 

 old volunteer had been established at a height of 237 centimeters just below 

 the dead tip of the 1918 growth, giving the tree a height of 300 centimeters. A 

 conspicuous brownish zone of parenchyma, developed shortly after the beginning 

 of the 1919 growth ring, could be traced from the apex of the growth of this 

 year, at the base of the dead 1918 tip, at an elevation of 237 centimeters, down 

 the stem to an elevation of 75 centimeters. At this point a faint zone of 

 parenchyma also showed in the beginning of the 1918 growth ring and could be 

 traced up the stem to an elevation of 200 centimeters, a point just below the apex 

 of the 1918 growth, where the stem had a diameter of but 2 millimeters. Beyond 

 this point the injury was not evident with a hand lens, but only in sections ex- 

 amined under the microscope. By means of a microscopic examination this zone 

 of parenchyma formation could be traced up to an elevation of 211 centimeters, 

 at which point the stem, consisting of only the 1918 growth, was but 1 millimeter 

 in diameter, or practically to the apex of the growth ring of that year. 



Through the kindness of J. A. Larsen, director of the Priest 

 River Experiment Station in Idaho, the writer was enabled to 

 examine and procure material for the study of a number of non- 

 indigenous conifers that showed the effects of repeated late-frost 

 injury. The trees had been grown to the transplant stage in Cali- 

 fornia and planted some years previously on an open bench at the 

 experiment station. The stock in question comprised young trees 

 of Pinus lainbertiana. Pseudotsuga taxifolia, Chamaecyparis law- 

 soniana, and Sequoia washing toniana, all of which except Pseudo- 

 tsuga taxifolia are nonindigenous to Idaho. All of these trees, 

 especially the two species mentioned last, exhibited an abnormally 

 compact and bushy form and owing to the repeated injury con- 

 tained frost rings in practically every growth ring. At. the time of 

 the examination all of the two species last mentioned, as well as a 

 large number of the first two species, were dead, due probably to 

 the combined action of the repeated late-frost injury and recent 

 drought injury. 



The young shoots, however, are by no means always killed back 

 by late frost. Not infrequently the shoots injured by frost may 

 remain alive throughout and still record the injury within their 

 tissues in the usual manner. In this form of late-frost injury the 

 terminal shoots as well as the corresponding lateral shoots sometimes 

 exhibit more or less of a characteristic permanent distortion, which 

 is accompanied by a frost-ring formation in the wood. While not 

 observed in any of the western frost-injured conifers which the 

 writer studied, this type of injury has been described by Hartig 

 (2) for Pinus sylvestris and has been observed by the writer in a 

 row of } T oung trees of Pinus densiflora, a Japanese species of dwarf 

 bushy pine grown in a nursery on the Mall, in Washington, D. C. 

 For the correlation of this form of injury with late frost and the 

 observations on the behavior of the trees immediately after the 

 freezing the writer is indebted to R. H. Colley and G. F. Gravatt, 

 of the Office of Investigations in Forest Pathology. 



From March 27 to 29, 1921, there occurred a general cold wave, 

 coming after a period of abnormally warm weather, which was very 

 destructive to the active vegetation over a large part of the country 

 east of the Mississippi River. On the day following this freeze, 

 March 30, it was observed that large numbers of the 1921 shoots 



