488 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



In soil-block tests^°* ^^ Porta incrassata, Porta monticola and Lenzites 

 trabea have been resistant to greensalt K, whereas Lentinus lepideus is 

 very susceptible. The writer interprets the results of these three types 

 of evaluation procedure, by soil-block, by %-inch stakes, and by posts 

 or poles to mean that: 



1. The conditions for decay, as far as Lenzites trabea are concerned, 

 are much more favorable in the soil-block culture bottle than they are 

 in the above ground part of a pole under normal outdoor exposure con- 

 ditions; 



2. The incidence of attack or infection at the ground line by Lenzites 

 trabea, Poria incrassata and Poria monticola at Gulfport is relatively 

 rare; and that 



3. The success of greensalt K in southern pine poles may be attributed 

 in large part to the susceptibility of the ubiquitous Lentinus lepideus to 

 the combination of salts in the greensalt preservative. 



Incidentally one may cite the following example of confirming results 

 in tests of another salt preservative. Harrow's ^^ experiments with soil- 

 block tests resulted in locating a threshold for zinc chloride on unweath- 

 ered blocks at 0.28 pounds per cubic foot (at treatment) for Lenzites 

 trabea, Madison 617 and 0.53 for Poria vaporaria. Richards and Addoms^^ 

 found approximately 0.25 for Madison 617, and approximately 0.50 for 

 Poria monticola, Madison 698. These two Porias are possibly the same 

 species. The similarity in the thresholds appears to be the definite result 

 of following the same technique, rather than a haphazard coincidence. 



The Evaluation of Pentachlorophenol 



The highly toxic properties of pentachlorophenol have been estab- 

 Ushed by exhaustive Petri dish agar toximetric tests. ^^ A 5 per cent 

 solution of penta in a light petroleum solvent is the preservative of 

 reference in the recommended standard test for evaluating oil-soluble 

 wood preservatives of the National Wood Manufacturers Association. ^^^ 

 This test, as pointed out previously, is an agar-block test. Duncan re- 

 ports*^ that threshold determinations based on soil-block tests of a 5 per 

 cent solution of penta in petroleum (cf . Tables V and VI) against Len- 

 zites trabea, a critical fungus for this preservative, have not varied more 

 than zhO.2 pounds from 4.8 pounds per cubic foot in 7 series of weath- 

 ered block experiments over a five-year period. Recent Bell Telephone 

 Laboratories' soil-block tests confirm this result, with the same fungus 

 and the same petroleum carrier. 



These results are confirmed at the Laboratories' Gulfport test plot 



