RESISTANCE OF CONIFERS TO CREOSOTE INJECTION. 25 



ducts themselves. Springwood was difficult to peuetrate but was sometimes 

 treated, especially in the zone where pressure was applied. 



In the sapwood, resin ducts occurred frequently that were not well pene- 

 trated, while the summerwood band, a few tracheids distant, was heavily 

 treated. The penetration appeared to follow first the very last-formed sum- 

 merwood tracheids of each year's growth. Later the second and third rows of 

 tracheids were penetrated and finally the entire summerwood band. Still 

 later slight penetration occurred in some of the springwood tracheids, but this 

 was comparatively rare. 



In the medullary rays neither the intermediate cells nor the ray parenchyma 

 were treated. The upper and lower ray cells, however, were very frequently 

 penetrated from the longitudinal summerwood tracheids, and these ray cells 

 extended through the longitudinal tracheids of the springwood without in any 

 way penetrating them. This whole phenomenon was not noted in any of the 

 species previously discussed. 



The cylinder-treated wood was penetrated in much the same manner as the 

 pieces treated in the penetrance apparatus. All summerwood was well treated, 

 and in the sapwood a considerable amount also of springwood. 



This wood, in common with most of the species previously discussed, becomes 

 discolored in the springwood several weeks after treatment. On close examina- 

 tion it was found that most of the discoloration was localized in the bordered 

 pits. It is not evident from present knowledge how this could be confined to 

 the pits without the remainder of the tracheids also becoming discolored. 



Eesin ducts were not an important factor in the treatment of this species. 

 The summerwood was penetrated very rapidly. The sapwood absorbed more 

 oil than the heartwood, chiefly because the former was more heavily treated 

 in the springwood. 



The ratio of average longitudinal to average radial or tangential penetration 

 can not be determined because the specimens were completely penetrated longi- 

 tudinally, but it was at least 120 times as great. 



WHITE SPRUCE (PICEA CANADENSIS). 



The growth rings of white spruce were broad; the summerwood was about 

 one-fourth the width of the springwood. Resin cells were never present. The 

 resin passages were few, large, and sometimes contained tyloses. The ducts of 

 the fusiform rays were surrounded by thick-walled epithelial cells. 



The average oven-dry weight of five heart specimens was 24 pounds per cubic 

 foot. 



The penetrance tests were made on heartwood only. The penetration took 

 place most quickly in the last-formed summer tracheids of the various growth 

 rings, and in most cases the summerwood as a whole was treated more quickly 

 than springwood. Near the point of pressure the springwood was partially 

 treated. Resin ducts in the specimens were so infrequent that they had little 

 effect upon penetration. Ray ducts were difficult to treat and appeared to aid 

 little in radial penetrations. 



The cylinder-treated sticks were penetrated similarly to those treated in 

 the penetrance apparatus. Resin ducts when present were usually treated, but 

 apparently they aided very little in the penetration of the tracheids surround- 

 ing them. Medullary ray tracheids were occasionally treated, but the pene- 

 tration was limited and took place with difficulty. The summerwood was 

 usually treated to the center of the stick. Often, however, zones occurred cover- 

 ing several growth rings in which the summerwood was not treated. When 

 the summerwood failed to be penetrated the springwood was not treated. In 



