EVALUATION OF WOOD PRESERVATIVES 



133 



The culture jars are wide mouth cyhndrical 8-ounce bottles, provided 

 with screw caps. The moisture content of the soil is predetermined on a 

 representative sample, and enough distilled water is placed in the bottle 

 so that when the soil is added its moisture content will be somewhat 

 above 40 per cent by weight. The bottles are filled approximately half- 

 full of screened field top soil — which means about 140 grams of an 

 oven-dried sandy loam. The soil handles better if it is reasonably dry 

 so that it can be poured through a suitable funnel; and putting the 

 water in bottles before one puts in the soil results in a practically clean 

 glass surface on the inside of the bottle above the soil level. 



Two southern pine sapwood feeder blocks, measuring 1 J^ inches in the 

 direction of the grain by % inch by approximately ^^2 inch (35 x 20 

 X 4.0-4.5 mm) are placed carefully on the flattened soil surface, as shown 

 in Fig. 1(a). The soil and feeder block setups are then steriHzed for one- 

 half hour at a pressure of 15 pounds per square inch, after which they 

 are allowed to cool in the autoclave. 



Inoculation is accomplished by carefully placing a piece of inoculum, 

 cut from a fresh Petri dish culture of what may be called a standard 

 test organism, at or near the middle of the feeder block surfaces. Under 



Fig 1— Four eight-ounce cylindrical bottles illuslrating the soil-block cultures: 

 (a) Bottle half-full of top soil, containing 40 per cent moisture on an oven-dry 

 soil basis, with two fiat feeder blocks of southern pine sapwood on top. (b) A 

 sixteen-day old culture ready to receive the impregnated southern pine sapwood 

 test blocks, (c) Two laboratory weathered test blocks from the same series treated 

 to a below threshold concentration of pentachlorophenol 0.051 lb dry penta/cu ft, 

 attacked by the test fungus, Lenzites trabea. (d) Two test blocks laboratory 

 weathered, treated to a retention of 0.194 lb dry penta/cu ft, near the threshold 

 retention, showing resistance to fungus attack. 



