RESISTANCE OF HAEDWOODS TO CBEOSOTE. 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. 



GROUP I. 



(Woods which treated easily in the tests.) 



Ring-porous tooods: 



Tyloses generally lacking — 



Slippery elm Ulmus pubescens, heartwood. 



Red oak Quercus rubra, heartwood. 



Chestnut oak Quercus prinus, heartwood. 



Tyloses scatteringly developed or thin walled — 



White ash Fraxinus am ericana, heartwood. 



Green ash Fraxinus lanceolata, heartwood. 



White elm Ulmus americana, heartwood. 



Hackberry Celtis occidentalis, sapwood. 



