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



The average oven-dry weight per cubic foot of six heart specimens was 

 30.5 pounds. 



Heartwood only of western larch was tested, as the sapwood is so thin that 

 suitable pieces were not obtainable. The resin ducts were comparatively easy 

 to penetrate, and isolated ones outside of the zone of longitudinal treatment 

 were very frequently penetrated through intersecting radial ducts. Certain 

 treated resin canals were closely examined and showed that : 



1. Where fusiform rays crossed summerwood bands the latter were not 

 treated. 



2. The fusiform rays frequently intersected treated longitudinal ducts and 

 usually contained creosote. 



3. The summerwood on each side of longitudinal resin ducts was treated 

 tangentially from one-eighth to one-fourth inch. 



4. Resin and creosote appeared to be forced away from the resin canal into 

 summerwood, but not often into springwood. 



The summerwood was completely penetrated in most of the pieces, while, as a 

 rule, the springwood was penetrated longitudinally about 1 inch only. 



Cylinder treatments also showed that summerwood was much more penetrable 

 than springwood. The relatively greater ease of penetration was probably due 

 to the resin ducts, as in every case the greatest penetrations were found to be in 

 the zone of a resin duct. Even without pressure the oil frequently penetrated 

 the ducts longitudinally as much as 6 inches. 



In heavily treated portions both springwood and summerwood were treated, 

 but the latter much more heavily than the former. 



It is known from other tests that the sapwood of this species is very easily 

 treated, and may be completely penetrated in both springwood and summer- 

 wood. 



TAMARACK (jLARIX LARICINA). 



The summerwood of tamarack was from one-fourth to one-half the width of 

 the springwood. Resin cells were few, and widely scattering on the outer face 

 of the summerwood. Resin passages were large and devoid of tyloses, and ran 

 in radial and longitudinal directions. 



The average oven-dry weight of six heart specimens was 32.5 pounds per cubic 

 foot. Only heartwood specimens were treated as the sapwood was too thin to 

 cut test specimens. 



Tamarack offered great resistance to penetration. While similar to western 

 larch in its microscopic structure, it was very different in its resistance to treat- 

 ment. Most of the resin ducts were impenetrable under the conditions of the 

 test. Longitudinally penetration occurred in 30 to 45 minutes, but only in a 

 few isolated ducts, and then it did not spread to the surrounding cells, except 

 near the point of pressure. The summerwood seemed to offer as much re- 

 sistance as did the springwood. 



Certain observations were made on treated sapwood of tamarack, which were 

 aside from the regular experiments. These observations showed that the sap- 

 wood was very easy to penetrate. Both the springwood and summerwood (in 

 the sap) were saturated with oil in a moderate treatment; the summerwood 

 usually seemed to have the heavier absorption. 



The average longitudinal penetration was 22 times the average radial and 

 tangential penetrations. 



