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



Radial resin ducts were found to be especially important. Where 

 these occurred the wood was usually penetrated radially from one- 

 fourth to three-fourths as far as longitudinally, and tangential pene- 

 tration could usually be disregarded. Where no radial ducts were 

 present, radial and tangential penetrations could be considered as 

 equal, and they were found to be between one-twentieth and one one- 

 hundred-twentieth of the longitudinal penetrations. 



2. Absorption curves (see Appendix) platted for the specimens 

 treated in the cylinder show that those species which were most 

 difficult to impregnate gave the most uniform absorption results, and 

 that the sapwood of those species containing resin ducts gave the 

 most erratic absorption results. They showed also that sapwood of 

 pines, as distinguished by its color from heartwood, was not always 

 easier to treat than the heartwood. The color line in the wood does 

 not necessarily separate the easily treated wood from the portions 

 treated with difficulty. Some sapwood treated like heartwood and 

 some heartwood treated like sapwood; all of these conditions are 

 possible in the same cross section of a tree. As a consequence of 

 this, the absorption curves for pines were, as a rule, very erratic, 

 especially the sapwood curves. 



3. The results obtained with a given species of wood can not 

 always be applied to another species, however similar in structure 

 the two may appear to be. This fact is strikingly evident in the 

 treatment of heartwood larch and tamarack. Even woods of the 

 same species show variations when grown under widely different 

 conditions, as, for example, western yellow pine from California 

 and from Montana. 



Detailed results of the tests on each species are given in the 

 Appendix. 



APPENDIX. 



DESCRIPTION OF SPECIMENS AND MANNER OF TREATMENT. 1 



YEW (TAXUS BREVIFOLIA ) . 



The summerwood in the yew specimens was equal to about one-fourth of 

 the width of the springwood. Resin cells and resin canals are entirely absent 

 in this species. 



The average oven-dry weight per cubic foot of eight heartwood specimens of 

 yew was 38.5 pounds. 



The penetration in both penetrance and cylinder treatments was found to 

 take place equally in springwood and summerwood. Radial and tangential 

 penetrations were also about equal. The average longitudinal penetration was 

 about 50 times the average radial or tangential penetrations. 



1 In describing the woods used in these tests the observations made on the specimens 

 are in some cases supplemented by remarks on the general characteristics of the species 

 taken from Penhallow's " North American Gymnosperms." 



