WOOD SOIL CONTACT CULTURE TECHNIQUE 115 



top soil than of that on the mixtures of sand and fuller's earth indicates 

 that the nutrients present in the soil were not all removed by the water 

 extraction. I'urther information was obtained by adding soil extract and 

 other nutrient solutions to the sand-fuller's earth mixtures. The following 

 materials were used: 



4500 grams of washed l^cach sand 

 900 grams of fuller's earth 

 300 ml. of soil extract 

 60 ml. of malt extract (2% water solution) 

 50 leached blocks 



vitamins Ri, Be and biotin (free acid) 

 stock mineral sclution of the following composition: 

 1.5 grams per liter of KH2PO4 

 1.0 gram per liter of MgS047H20 

 plus the following elements in parts per million: 



0.02 Cu, 0.01 Mn, 0.005 B, 0.10 Fe, 0.01 Mo, 0.09 Zn 

 pure cultuies of the fungus Poria incrassata 

 42 eight-ounce bottles, screw capped (12 cm. high by 6 cm. diameter) 

 maltose 



Procedure: 



The sand and fuller's earth in the proportions mentioned above were 

 mixed in a porcelain jar on a ball mill for six hours. The blocks were 

 leached for two years with weekly changes of distilled water, using 50 ml. 

 of distilled water for each block. Before the test, the blocks were oven- 

 dried to constant weight at 105°C. and a volume measurement was made 

 by mercury displacement method. The volume at liber saturation was 

 calculated from the oven-dry volume according to the formula: X'olume 

 at liber saturation = Oven-dry volume + 0.25 X oven-dr>^ weight. 



One hundred grams of the soil moistened with 20 ml. of the appropriate 

 nutrient solution (Table 1) was placed in an eight-ounce bottle for each 

 block. The weighed block was pushed into the soil with a cross-section of 

 the block facing upward until the top of the block was level with the soil. 



The bottles were capped and autoclaved for 20 minutes at 20 pounds' 

 pressure. After sterilization and cooling, an inoculum from a pure culture 

 of the fungus Poria incrassata was placed on the top of each block. The 

 bottles were then placed in a controlled temperature room (26°-28°C., 

 relative humidity 90^95%) for 16 weeks. 



At the end of this time the blocks, brushed free of soil and mjcelia, were 

 weighed immediately, and the volume was measured. Finally, the blocks 

 were again oven-dried to constant weight and the volume was measured 

 again. 



The average volume at fiber saturation of the 42 blocks calculated from 

 the initial volume when oven-dry was found to be 7.24 cc, and the linal 

 average volume when removed from the test was 7.26 cc. Xo shrinkage 

 took place until the blocks were oven-dried, and then tlic distortion became 



