10 BULLETIN 101, U. S. DEPARTMENT OF AGEICULTUBE. 



PENETRATION IN SAPWOOD AND HEARTWOOD. 



The sapwood was much more easily penetrated than the heartwood 

 in those species having highly developed resin systems, such as Doug- 

 las fir, larch, tamarack, and the spruces and pines. Species having 

 no resin ducts treated but little better in the sapwood or outer portion 

 than in the heartwood or inner portion. But the latter tendency does 

 not always hold, since cedars, cypresses, and other woods (which were 

 not here tested) are known to be more easily treated in the sapwood. 

 These species have, however, a distinct color difference between heart- 

 wood and sapwood. 



It is true that the harder and more insoluble resin in the ducts of 

 the heartwood adds to the difficulty of penetrating heartwood. The 

 great ease of penetration of the sapwood of pines, spruces, and other 

 species seemed to be a property of the nonresin structure which, in 

 conjunction with the resin ducts, rendered these woods very suscep- 

 tible to treatment. 



PENETRATION IN SPRINGWOOD AND SUMMERWOOD. 



It was found in most species that the summerwood was more pene- 

 trable than the springwood. But this rule did not hold for red- 

 wood, yew, and tamarack. Redwood not only treated more easily in 

 the springwood, but the summerwood was scarcely penetrated. In 

 the yew and tamarack the springwood and summerwood were about 

 equally resistant. In all other species tested the dense summerwood 

 was the portion penetrated first, and usually the tracheids last 

 formed, those with the thickest walls and smallest lumen, were the 

 most penetrable. 



The summerwood not only permitted the oil to enter more quickly 

 and penetrate farther than did the springwood, but actually absorbed 

 a greater amount of it. This last fact was indicated by the difference 

 in color between treated summerwood and treated springwood. It 

 was shown also in the case of a treated specimen of loblolly pine, in 

 which, by actual determination, the summerwood contained 80 per 

 cent more oil than the springwood. 



In no case was any stick of wood absolutely impermeable. The 

 springwood of the most impermeable species could always be pene- 

 trated longitudinally for three or more tracheids from the point of 

 application of the pressure. (PL VII, fig. 1.) * 



PENETRATION IN THE MEDULLARY RAYS. 



Except in the case of ray ducts the medullary rays, as a rule, were 

 not penetrated. In some of the spruces, however, the upper and 

 lower ray tracheids were penetrated and in some of the pines 

 the entire ray. In no case except the spruces and pines was any 

 penetration noted in the rays unless the specimen was very heavily 

 treated. 



