6 BULLETIN 1131, U. S. DEPARTMENT OF AGRICULTURE. 



by him any pronounced permanent distortion of the living shoots 

 which would indicate injury by late frost, except in the case of 

 Pinus densiflora Sieb. and Zucc, a Japanese species which will be 

 considered later. 



In every case where the terminal growth had been killed, a narrow 

 brownish zone of abnormal tissue, or frost ring, could be traced from 

 the base of the dead shoot down the stem for a distance of several 

 inches, or often for several feet in the case of saplings. This zone of 

 abnormal tissue, which has the appearance of a brownish stripe in 

 sections of the stem, usually occurred in the immediate beginning of 

 the growth ring or else a short distance beyond the outer limit of the 

 growth ring of the preceding year. In the latter case it gave the ap- 

 pearance of a double ring formation, especially when the growth rings 

 were rather narrow. As a rule, the action of late frost manifests 

 itself in a closed ring, although occasionally the zone of injury ap- 

 pears only on one side of the stem. In no case of late- frost injury 

 observed by the writer was any external sign of mechanical injury to 

 the bark visible. 



Measurements of the linear extent of the frost rings were made 

 in only a few instances where larger trees were involved, since this 

 point was not deemed of any particular importance. In general, it 

 may be said that in the smaller trees they usually extend down to 

 or nearly to the ground line. In the larger trees, however, they 

 terminate rather abruptly as the older and therefore better protected 

 portion of the stem is reached. While the writer has observed the 

 occurrence of frost rings in the outer growth rings of saplings of 

 Larix occidentalis and Pseudotsuga taxifolia 2 inches in diameter, 

 he has not observed their occurrence in coniferous stems of larger 

 size at the time of the injury. Frost-ring formation, however, often 

 occurs in larger stems of fruit trees that are subject to various forms 

 of frost injury. The latter in general, however, perhaps due in part 

 to the cultural practices employed, are more susceptible to frost injury 

 than the coniferous trees. Detailed stem-analysis data are recorded 

 for four saplings of Larix occidentalis from an area in which frost 

 rings were found to be especially numerous, as mentioned below. 



Stem Analysis of Larix Occidentalis Saplings with Feost Rings, Cut at 

 Ione, Wash., August 24, 1920. 



Tree No. 1. — The tip of the original leader formed in 1918 had been killed and 

 was dead down to an elevation of 223 centimeters above the ground, at which 

 point a 2-year-old volunteer had developed subsequent to the injury, giving the 

 sapling a total height of 278 centimeters. A conspicuous brownish zone of 

 parenchyma wood, located in the 1919 growth ring and developed very soon 

 after the initiation of the growth of that year (PL II, C), could be traced down 

 the stem to an elevation of 65 centimeters above the ground, at which point it 

 was no longer apparent -under a hand lens. A section of the wood at this point 

 showed under the microscope practically no distortion of the wood elements. 



Tree No. 2. — Another sapling, with a height of 365 centimeters and with no 

 evidence of any external injury or dead terminal shoot, showed upon dissection a 

 similar brownish zone of parenchyma formed shortly after the beginning of 

 the 1919 growth ring. This line of parenchyma could be traced from the apex 

 of tbe 1918 growth, at an elevation of 300 centimeters, down the stem to an 

 elevation of 175 centimeters, below which point it was no longer in evidence. 



Tree No. 3. — In this case the original leader had been killed, and a volunteer 

 leader 2 years old had been put out at a height of 158 centimeters, just below 

 the dead tip of the 1918 growth. A brownish zone of parenchyma, formed 

 shortly after the beginning of the 1919 growth ring, was traceable down the stem 



