Bui. 1131, U. S. Dept. of Agriculture, 



Plate V. 



Frost Injury to Pinus monticola and Pinus albicaulis. 



A .—Transverse section through a stem of Pinus monticola, showing the termination of the pre- 

 ceding annual ring (at the outer margin of the resin canal at bottom of picture) and three frost 

 rings occurring in the early portion of the succeeding growth ring. (X135.) B. — Transverse 

 section through a frost ring iu Pinus albicaulis, showing the crumpling of the wood cells that 

 were but slightly lignified at the time of freezing and the formation of a radial cleft (at the left) 

 which has become filled by large-celled parenchyma, (x 135.) 



