RESISTANCE OF CONIFERS TO CREOSOTE INJECTION. 15 



GROUPING WITH RESPECT TO SUITABILITY FOR TREATMENT IN PARTICULAR 



FORMS. 



In this sort of grouping the main considerations are whether or 

 not the sapwood treats more easily than the heartwood, and whether 

 the wood can be easily penetrated radially. Round forms, such as 

 fence posts, mine props, telephone posts, and piling constitute one 

 class, while sawed heartwood ties, bridge timbers, sawed mine tim- 

 bers, and other dimension timbers constitute a second class. Paving 

 blocks are considered separately. 



ROUND TIMBERS. 



The penetration of the sapwood in round timbers is more impor- 

 tant than that of the heartwood, since the latter is inclosed by the 

 former. Railroad ties in which the heartwood is not exposed by 

 hewing or sawing may be considered as round timbers. Since round 

 timbers to be treated must be penetrated radially through the resin 

 ducts it is essential that all of the bark be removed before treatment. 

 The results obtained in these experiments and the experience of the 

 Forest Service generally indicate that the following species may be 

 successfully treated in the round form : x 



Engelmami spruce. 

 Douglas fir. 

 Tamarack. 

 Western larch. 

 . All of the pines. 



Species which received practically no radial penetration and, there- 

 fore, are not well adapted to treatment in the form of round timbers, 

 include the following: 



Alpine fir. Eastern hemlock. 



Yew. Western hemlock. 



Noble fir. Redwood. 



White fir. Sitka spruce. 



DIMENSION TIMBERS. 



In dimension timbers the treatment of the heartwood is of chief 

 importance, since the sapwood is generally removed at least from 

 part of the faces. These experiments indicate that — 



Species in Class I are entirely unsuitable for treatment in the form 

 of dimension timber. 



Species in Class II are also unsuitable for this purpose, but may 

 be treated under very severe pressure. 



Species in Class III are net especially suitable for treatment as 

 dimension timbers, but satisfactory results are being obtained in 

 practice. 



1 Probably also the cedars and cypresses. No data have been obtained on these, 

 however. 



