406 Forestry Quarterly. 



Microscopic Method. 



The wood of all trees native to the temperate zone is clearly 

 marked on transverse section by circular bands which are known 

 as annual layers or rings. These annual rings are due to the 

 fact that the cells composing them are not of the same structure 

 throughout the whole ring. In spring and early summer the 

 cells are large, thin-walled, and in the case of broadleaf trees, 

 traversed by many water-conducting vessels. Toward the end 

 of the vegetative season, the cells become small, thick-walled and 

 compact, and in the broadleaf trees the number and size of fibro- 

 vascular bundles decrease. At the beginning of the following 

 vegetative season, the new layers begin abruptly again with large 

 cells, and this sudden transition from one kind of cell to another 

 makes the wood appear in the form of clearly defined rings. The 

 exact cause of this structural difference in the "summer" and 

 "winter" wood is not fully known, but it is present in all trees of 

 the temperate zones or climates with periodic changes of season. 



It is evident therefore that the stage of development of the last 

 ring furnishes a means of determining the time at which the tree 

 was cut. If the last layer of pine wood for instance, examined 

 under the microscope or magnifying glass, shows only large, 

 hexagonal, translucent cells, one may infer with certainty that 

 the tree was cut during the early part of the vegetative season ; 

 if the last layer in addition to large hexagonal cells contains also 

 a fringe of small, compact, elliptical, whitish-yellow cells, it is a 

 sure indication that the tree was cut in the latter part of the 

 vegetative season, or, if the layer of winter wood elements is large, 

 that it was cut after the termination of the vegetative period. 



This periodicity of the seasons marked on the wood by annual 

 rings with their characteristic "summer" and "winter" wood, 

 served as a basis for a Russian civil engineer, P. E. Rashevsky, 

 to develop a practical and accurate way of determining the time 

 at which timber was cut. During the 20 years of his service 

 as civil engineer on one of the Government railroads in western 

 Russia, he became convinced that ties cut in summer did not give 

 the same service as ties cut in winter ; yet he was powerless to 

 make the contractors live up to the stipulation that all ties deliv- 

 ered to the railroads should be only of winter cut, since there was 

 no accurate way of telling this at the time of inspection at the 



