4 BULLETIN 101, U. S. DEPARTMENT OF AGRICULTURE. 



BESTN CANAES. 



In many species numerous large openings known as " resin canals " 

 exist. (PL I.) These passages are intercellular spaces, surrounded 

 by so-called " epithelial cells," the chief sources of resin production in 

 the tree. In a less number of species these canals occur within the 

 medullary rays, there known as " fusiform rays." These radial canals 

 intersect the longitudinal ones and thus form a partially complete 

 network of resin ducts penetrating all portions of the wood. Resin 

 ducts in pines are sometimes wholly or partially blocked by growths 

 called tyloses. 



DISTRIBUTION OF BESIN STEUCTUEES. 



With very few exceptions, all of the conifers contain either resin 

 cells or resin canals, and some species contain both. The distribu- 

 tion of resin cells varies in different species; in some they are scat- 

 tered through the wood, while in others they are concentrated in zones. 

 The character and number of the resin canals also vary greatly. 

 Those in some species, as in Douglas fir, are few in number, are small, 

 and have frequent constrictions tending to close the canal; those in 

 other species, as in longleaf pine, are abundant, large, and entirely 

 without constrictions. 



EXPERIMENTAL METHODS. 



The presence of resin canals and cells in the wood and the character 

 of these structures at once suggest that they may have a considerable 

 influence on the manner in which the wood takes impregnation with 

 preservatives. A considerable portion of the experimental work was 

 given to determining the extent of this influence. 



The resistance of the wood to treatment was determined by two 

 forms of tests: (1) by applying the creosote to a sma.ll area on a 

 specimen and measuring the penetration in different directions ; and 

 (2) by impregnation in a treating cylinder. In the latter tests blocks 

 from each of the species were treated together in the same run. 



APPARATUS. 



The " penetrance apparatus," illustrated in figure 2, was designed 

 for the first class of tests. The wood under test, which had a 1-inch 

 hole bored in it, was clamped against the open end of the pipe A lead- 

 ing to the bottom of a pressure tank B. The pipe and lower portion 

 of the tank were filled with creosote. Pipe C, opening into the top of 

 the tank, was connected with an air reservoir in which a pressure 

 was maintained. When desired, air under pressure was turned into 

 tank B, which thus placed the preservative under pressure. The 

 apparatus was surrounded by a wooden oven, as shown, with double 



