16 BULLETIN 606,- U. S. DEPARTMENT OF AGRICULTURE. 
possibly because of the presence of infiltrated substances. The 
medullary rays were practically impenetrated. Heartwood speci- 
mens treated in the cylinder rarely showed any more than a very 
slight end penetration. 
RELATION OF GROUPING TO COMMERCIAL TREATMENT. 
The form in which a timber is treated determines to a large extent 
the relative importance of securing a penetration in the sapwood or 
in the heartwood. Penetration of the sapwood is of principal im- 
portance in the treatment of material in round forms, such as posts 
and telephone poles, as in this case it is the sapwood that is exposed 
to the attack of fungi. Although tests could not be made on sap- 
wood from each of the species used, the sapwood of practically all 
of these woods is known to be fairly easy to penetrate in both longi- 
tudinal and radial directions. Even those species which were most 
difficult to penetrate in the heartwood took treatment comparatively 
well in the sapwood. 
In the treatment of sawed or split timbers, which generally have 
little or no sapwood, the penetration of the heartwood becomes of 
chief importance. The results of the experiments indicate that woods 
in Group I are well adapted for treatment in dimension form, since 
the heartwood as well as the sapwood of the species was penetrated 
with comparative ease. Where radial penetration of the heartwood 
is of special importance, as in the open-tank treatment of split tim- 
bers for fence posts, particular attention should be given to the ease 
or difficulty with which the wood prosenchyma can be penetrated. 
The heartwood of some of the woods in Group II would probably 
be somewhat difficult to penetrate thoroughly and evenly in pressure 
treatments. This difficulty would be more apparent in the timbers 
of larger size, such as railroad ties, mine timbers, etc. With one or 
two exceptions, hickory, for example, radial penetration was small in 
species of this group. The heartwood of the species given in Group 
III would appear to be difficult to treat. Specimens of this group 
treated in the penetrance apparatus and in the cylinder showed no 
appreciable radial penetration, and onh r a slight longitudinal pene- 
tration at the ends. 
CONCLUSIONS. 
There are several very important factors other than the wood struc- 
ture which, in commercial work, influence the absorption and pene- 
tration of preservative. Some of these are the natural variability of 
the wood, even in the same species, the moisture content when treated, 
the method of seasoning and treatment adopted, and the character 
of the preservative used. In order to study the true effects of the 
