Small blocks of ponderosa pine (Pinus ponderosa Laws) chemically modified with butylene oxide to three different weight gains were exposed for 6 weeks in unsterile soil. Severe surface decay caused by soft rot fungi and tunnelling bacteria was observed in blocks with 8 weight percent gain. The soft rot attack was restricted to the outer parts of the radial walls in the latewood tracheids. Bacterial attack occurred both in the radial and tangential walls. Very few soft rot cavities were found in blocks with 15 weight percent gain. Some attack by tunnelling bacteria was observed in the outermost parts of the radial walls in the latewood tracheids. Wood blocks with 23.7 weight percent gain showed no signs of attack. A solution of crystal violet was used for examining pathways in ponderosa pine wood. The results indicate that the uneven distribution of cavities is due to improper penetration of the modifying agents into the outer parts of the radial walls in the latewood tracheids.

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