RESISTANCE OF HARDWOODS TO CREOSOTE. 15 



coming out at the side of the specimens instead of passing through 

 to the end. 



The pressure and time of treatment are not comparable to com- 

 mercial treating-plant conditions because of the size and dry condi- 

 tion of the specimens. 



The woods included in Group I were all comparatively free from 

 tyloses and other obstructions in the vessels. Wood gums were pres- 

 ent to only a slight extent ; for example, in birch and maple. All of 

 the species included in this group therefore treated very easily. Ex- 

 amples of species which exhibit very clearly the characteristic open 

 structure are red oak. chestnut oak, and slippery elm. The wood 

 prosenchyma, or fibrous part of the wood substance, was also usually 

 well treated in woods of this group. The medullary rays and other 

 parenchyma cells received, as a rule, little treatment, although ex- 

 ceptions were noted in woods like ash and birch where creosote also 

 penetrated this part of the wood structure. 



While numerous tyloses were found in the ashes, their influence 

 on penetration of these species was not so important as in most of 

 the other species in which tyloses were present. This was due to 

 the fact that the tyloses were not fully developed in the vessels, and 

 that they were also very often thin-walled and somewhat variable. 



Group II. — With the exception of hickory, the species in Group II 

 showed incomplete and variable penetrations in all of the cylinder 

 treatments. The average absorptions obtained in these treatments 

 were between 7 and 10 pounds per cubic foot in all of the species 

 except silver maple, black willow, and largetooth aspen. In these 

 three woods the absorptions were somewhat higher, but in the indi- 

 vidual specimens they were extremely variable and the penetrations 

 were very irregular on account of the uneven distribution of gummy 

 substances in the maple and tyloses in the other two species. In all 

 of the species of this group the average longitudinal penetrations 

 obtained in the penetrance tests were between 1 and 8 inches. 



Tyloses were present in all the species in this group except the 

 two maples, but with few exceptions they did not completely close 

 the vessels. Hickory was one of the few cases in which it was 

 possible to obtain a fairly good penetration, although the pores were 

 completely blocked with tyloses. In this species the treatment took 

 place through the wood prosenchyma, which was quite permeable. 



Group III. — The average absorptions in the cylinder experiments 

 were less than 6 pounds per cubic foot, and the average longitudinal 

 penetrations obtained in the penetrance tests were less than 2| inches 

 in all of the species classed in Group III. In most of these species 

 the vessels were, as a rule, completely closed by an abundant growth 

 of tyloses, which effectively retarded the entrance of creosote. The 

 wood prosenchyma of these species was also very difficult to treat, 



