RESISTANCE OF CONIFERS TO CREOSOTE INJECTION. 21 



REDWOOD (SEQUOIA SEMPERVIRENS ) . 



In the redwood the summerwood was about one-third the width of the spring- 

 wood. The latter was very open, with thin-walled tracheids. The resin cells 

 were rather large, numerous, and scattered throughout the springwood. 



Resin cysts, or aggregates of resin cells, were sometimes contiguous and 

 coalescent and formed extended tangential series in the initial growth of the 

 springwood of distant-growth rings. Often the cysts were separated longitudi- 

 nally only by a wall of resin cells. Tyloses were sometimes present in the cysts. 



The average oven-dry weight per cubic foot of four heart specimens was 20 

 pounds, and of seven sap specimens 19.3 pounds. 



Penetration in general took place more readily in the springwood than in 

 the summerwood, but the maximum penetrations were in the one to three last- 

 formed summerwood tracheids and in the two or more first-formed springwood 

 tracheids; that is, along the outer face of the summerwood in the zone of the 

 resinous cells and cysts. In the portions treated most heavily the summerwood 

 band was treated throughout, but usually it was penetrated very slightly. 



The character of the penetrations in the cylinder treatments was very 

 similar to that in the penetrance tests. Near the end of the stick the entire 

 springwood of nearly every ring was penetrated, but near the center only the 

 first-formed springwood tracheids were treated. The summerwood was usually 

 treated for only a short distance from the ends. 



In the sapwood penetration was somewhat quicker and absorption a trifle 

 greater than in the heartwood. But these differences were so slight that they 

 may be disregarded. 



Radial and tangential penetrations were about equal. This indicated that 

 tangentially extended series of resin cysts did not influence appreciably tangen- 

 tial penetration. The average longitudinal penetration was about 50 times 

 greater than the average radial or tangential penetrations. 



The influence of the resin structure was apparent in redwood. The creosote 

 followed the resin zone more readily than the surrounding wood structure. A 

 peculiarity of redwood was that the springwood was penetrated more easily 

 than the summerwood, whereas with most other species the summerwood was 

 more easily penetrated than the springwood. 



WESTERN HEMLOCK (TSTTGA HETEROPHYLLA) . 



The growth rings of western hemlock were narrow, with prominent summer- 

 wood bands usually about equal in width to the springwood, which consisted of 

 large and thin-walled tracheids. 



The average oven-dry weight per cubic foot of six heart specimens was 27 

 pounds, and of six sap specimens 28 pounds. 



Resin cells were very prominent on the outer face of the summerwood. These 

 sometimes united to form an imperfect resin passage. In other respects the 

 western hemlock specimens were structurally similar to eastern hemlock. 



Penetration took place more readily in the summerwood than in the spring- 

 wood. In most cases the resinous portion (on the outer face of the summer- 

 wood) seemed to be penetrated first, the oil passing for a very short distance 

 from this zone radially into both the summerwood and springwood. The sum- 

 merwood band as a whole treated almost as easily as the resinous zone, and in 

 many growth rings the summerwood was treated while the resin canals were 

 untreated. The springwood was also uniformly penetrated, but not as far nor 

 as heavily as the summerwood. 



