RESISTANCE CF HARDWOODS TO CREOSOTE. „ 13 
tooth aspen, naturally show less uniformity in the relation between 
penetration and absorption. A more constant relation between these 
factors is evident in species, such as basswood and tupelo gum, which 
take treatment both in vessels and in the wood substance. 
Detailed results of the tests and data on each species are given in 
the Appendix. 
GROUPING OF HARDWOODS FOR TREATMENT. 
A classification of the species studied in this investigation into 
three groups according to the ease or difficulty of penetration has 
been attempted. This classification is based on the results obtained 
in the penetrance and cylinder tests and upon the structural char- 
acteristics as determined by a microscopic examination, and is in- 
tended only as an aid in the commercial grouping of such woods for 
treatment. The heartwood and sapwood are here considered sepa- 
rately, but in commercial treating plant operations the same stick 
often contains both: so the groups which are given may not be the 
ones which must be used in practice. For example, tupelo gum and 
red oak ties, both classed as easily treatable species, are not grouped 
together during treatment because the tupelo gum usually contains 
more sapwood. 
Any grouping of species for preservative treatment must be a some- 
what arbitrary classification. It is difficult to determine where the 
line should be drawn separating species of one group from those of 
another. However, when the classifications are taken as a whole 
there is a very distinct difference in the ease or difficulty with which 
the species of one group took treatment as compared with those of 
another group. Furthermore, the results obtained in the penetrance 
and absorption experiments correspond quite well in most cases with 
what would be expected • from the structure of the various species. 
The grouping effected may be useful in giving an idea of what to 
expect of species unfamiliar to the reader, in comparison with species 
with which he is familiar. 
GE0T7P I. 
(Woods which treated easily in the tests.) 
Ring-porous ivoods: 
Tyloses generally lacking — 
Slippery elm Ulmus puhescens-, heartwood. 
Red oak Quercus rubra, heartwood. 
Chestnut oak Quercus prinus, heartwood. 
Tyloses scatter ingly developed or thin walled — 
White ash Fraxinus americana, heartwood. 
Green ash Fraxinus lanceolaia, heartwood. 
White elm Ulmus americana, heartwood. 
Hackberry Celtis occidcntalis, sapwood. 
