WOOD SOIL CONTACT CULTURE TECHNIQUE 105 



decayed more rapidly and more completely than in any previous liboratory 

 test. Preliminary experiments were devised to ascertain the factors re- 

 sponsible for the accelerated decay and to establish optimum conditions for 

 growth of fungi in laboratory tests of wood preservatives. As a result of 

 this exploratory work a laboratoiy technique was devised which permitted 

 study of these factors and which offered a convenient means of evaluating 

 toxicity and preservative properties of chemical compounds. Further in- 

 vestigation was made on the effect of nutrients and nutrilites in the soil, 

 temperature, and the moisture content of the wood. Parallel with this 

 laboratory investigation, a study was made of the fungus attack on wood 

 under climatic conditions very favorable for decay at Gulf port, Mississippi. 



IxiTLVL Experiments and Results 



As a preliminary step, the moisture content of the soil from the termite 

 colonies was determined by oven-drying 100-gram samples. This was found 

 to average 22% of the oven-dry weight of the soil. Tests with several soils 

 showed that approximately the same moisture content could be obtained by 

 merely adding to dry soil just enough water to make the mixture cohere when 

 squeezed in the hand. 



A one-hundred-gram sample of moist soil was placed in each of 24 large- 

 mouthed, eight-ounce, screw-capped bottles (12 cm. high and 6 cm. in 

 diameter). A weighed oven-dry block of southern pine sapwood, 2x2x2 

 cm., was pushed to a depth of about 2 cm. into the soil in each bottle. The 

 caps were put on, and the preparations were sterilized for 30 minutes at 15 

 pounds' pressure in an autoclave. After cooling, the block in each of twelve 

 of the bottles was inoculated with a pure culture of one of seven common 

 wood-destorying fungi — Lentinus lepideus, Fomes rosetis, Poria microspora* 

 Polyporus vaporarius, Coniophora cercbella, Poria incrassala, and Lenzites 

 irabea. Twelve bottles, not inoculated, were used for moisture determina- 

 tions. 



The bottles were then placed in an incubator maintained at 26°-28°C. 

 At the end of each month three of the bottles inoculated with each fungus 

 were taken from the incubator. Each block was removed from the soil and 

 weighed immediately; it was then allowed to dry in an oven at 105''-110°C. 

 to a constant weight. The average percentage loss in dry weight due to 

 decay was calculated. The results, recorded in Fig. 1, show that the very 

 rapid decay of wooden blocks in contact with the soil is not the result of any 

 one particularly active fungus. Each of the seven species produced ex- 

 ceedingly rapid decay under the conditions of the soil assay. 



♦This fungus was designated BTL U-10 until recently identified as Poria microspora 

 by Miss Mildred K. Nobles, Dcpt. of Agriculture, Ottawa, Canada, 19-13. (See Bibliog- 

 graphy at end of paper.) 



