WOOD SOIL CONTACT CULTURE TECHNIQUE 



117 



drates are destroyed. There is a slight indication that the vitamin mixtures 

 promote decay but the effect as measured by the weight loss is not very 

 pronounced. The basic mineral solution which was used in this experiment 

 promoted only slightly more decay than the distilled water. While the 

 results are not included in the table, it may be stated that leaching of the 

 blocks had no apparent effect on decay when compared with unleached 

 blocks. 



Influence of Temperature on Decay 



Most of the early work in the Bell Telephone Laboratories was conducted 

 by the petri dish method at temperatures in the range 26°-28°C., following 

 the recommendations of Richards, 1923. But certain fungi, including 

 MeruUus lachrymans, failed to grow at this temperature. When several 

 inocula of Merulius lachrymans that had failed to grow at 26°-28°C. were 

 transplanted to sterile blocks, according to the earlier sapwood-water tech- 

 nique, the loss in weight due to decay after six months averaged 34% at 

 21°C. and only 7% at 26°-28°C. 



An experiment was planned to test the influence of a wide range of tem- 

 peratures on the decay of wood in the soil contact assay method. Four 

 kinds of fungi were established under sterile conditions on untreated wood 

 slabs laid on moist garden soil. An abundant growth of the fungi was 

 secured within one to two months. Cubes of sapwood were placed on the 

 \'igorously growing mycelia, both of which had been conditioned by exposure 

 overnight to the various temperatures. Sterile soil, also conditioned to 

 the temperatures, was used to cover the blocks. After 15 weeks' exposure, 

 the results were as follows: 



Poria incrassala 



Polyporiis vaporarius 

 Poria nncrospora . . . . 

 BTL-U-11 



Average Weight Loss in Per Cent 



The results indicate that the standard temperature, 26°-28°C., was optimum 

 for the four fungi tested. No decay was produced by any of the fungi at 

 0°C. A temperature of 35°C. was too high for active decay; in the case of 

 Poria microspora, for instance, only a single block was attacked. The 

 series at 35°C. was repeated because the soil in some of the bottles seemed 

 to have become rather dry, although the blocks contained 30% moisture. 

 In the new series the humidity was maintained at 76% around the bottles 

 to reduce loss of water, and three more organisms were used. The results 



