138 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



21 



growth of the test fungus. Breazzano thoroughly saturated the sand 

 base in his test cultures. Leutritz and Harrow^^' ^^ working with tightly 

 closed culture jars found a 25 per cent level in the soil to be satisfactory. 

 Flerov and Popov state after special control tests "that replacement 

 of (the) sand by soil had no effect on the results of the tests and only 

 shortened their duration." Duncan'* has found from her tests that vari- 

 ations in moisture content and soil type affect the degree of fungus 

 attack only and that they do not change the determination of the treat- 

 ment threshold concentration in any given set of test blocks. 



Even-Aged Cultures 



The thickness of the feeder blocks has been gradually increased to 

 about Jf 6 inch, or between 4 and 4.5 millimeters. This provides food 

 for the fungus to estabhsh itseff in the bottle. The inoculum pieces are 

 roughly 1 cm square, cut from Petri dish cultures that are 15 zb 1 days 

 old. The planting routine is carefully scheduled so that even-aged soil- 

 block cultures — 13-15 days — are ready to receive the treated blocks 

 when the latter are ready to be placed in test. This principle of using 

 even-aged cultures has been stressed by the Madison investigators, and 

 it is considered to be a factor of major importance in the proper culture 

 technique. 



Standard Test Organisms 



There have been continuous discussions since the beginning of labora- 

 tory tests in Europe, as well as in this country, about what test organ- 

 isms should be used. Conforming to the experience and practice at 

 Madison the following three numbered strains of wood-destroying fungi 

 are recognized as the ''standard" strains for the testing of oil type pre- 

 servatives in coniferous wood : 



Lentinus lepideuSy Madison 534 

 Lenzites trabea, Madison 617 

 Poria monticola, Madison 698 



All three are known to be associated with the decay of treated timber. 

 Lentinus lepideus is particularly tolerant of creosote,^^' ^^ and relatively 

 susceptible to pentachlorophenol. It has frequently been isolated from 

 decaying creosoted southern pine poles and other creosoted coniferous 

 timber in contact with the ground. Lenzites trabea is generally an ''above 

 ground" fungus. It also has been isolated from decaying creosoted tim- 

 ber; and it is the principal cause of "shell rot" in the above ground sap- 



