RESISTANCE OF CONIFERS TO CREOSOTE INJECTION. 17 



No satisfactory theory has yet been offered to explain the penetra- 

 tion of wood by creosote. The following observations, based on the 

 experiments described in this bulletin, indicate the variety of phe- 

 nomena which such a theory would have to take into account. 1 



1. The summerwood in the conifers was, as a rule, easier to pene- 

 trate than the springwood; but exceptions were noted, as (Sequoia- 

 washing tonia) , which treated more easily in the springwood. 



2. In the pines the summerwood was usually well penetrated, 

 but the springwood penetrations were very erratic, often taking 

 place very readily in some portions of the wood and with great diffi- 

 culty in other portions of the same piece. (See PI. IV, fig. 2.) 



3. In most cases the resistance to penetration was least in the 

 last-formed summer tracheids (having the thickest walls and the 

 smallest cell cavities), and was greatest in the first-formed spring 

 tracheids (having the thinnest walls and the largest cell cavities). 



4. The color of the creosote oil in the springwood was often trans- 

 parent and amber, while in the summerwood it was very dark. 



5. In springwood apparently untreated the bordered pits fre- 

 quently were strongly discolored and seemed to contain creosote. 



6. In the pines, spruces, sequoia, larches, and Douglas fir the sap- 

 wood was more penetrable than the heartwood. In eastern and 

 western hemlock and in the firs the sapwood and the heartwood were 

 about equally penetrable. 



7. As a rule, the medullary rays had no influence on penetrance, 

 except when they contained resin ducts. Then they were usually 

 very difficult to penetrate, but in Picea certain tracheids of the 

 rays were readily treated, the upper and lower cells being usually 

 the first. Frequently from these rays one or more longitudinal 

 spring tracheids were penetrated. Sometimes all of the ray cells 

 were penetrated, but never as heavily as the summerwood tracheids, 



8. Of two sticks of wood similarly treated one was split immedi- 

 ately after treatment and the other several weeks later. They dif- 

 fered greatly in appearance. Springwood adjacent to treated sum- 

 merwood in the first piece was apparently untreated, but in the 

 second piece showed a marked discoloration. Microscopic examina- 

 tion of the latter showed that the cell walls were uniformly dis- 

 colored. 



CONCLUSIONS. 



The following conclusions were drawn as a result of the test* 

 described in this report : 



1. Radial and longitudinal resin ducts penetrate intimately the 

 interior of the wood and thus form passages for the preservative. 



1 Irving W. Bailey has recently published a paper in Vol. XI, No. 1, of the Forestry 

 Quarterly which throws considerable light on this subject. 



41702°— Bull. 101—14 3 



