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 t}^loses 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-wailed 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 4 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 II L — 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 J 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, 
