It was noted that the undergrowth under a stand of Robinia Pseudo-Acacia was sparse as compared with that under an adjoining area dominated by elms, oaks and hickories. It was thought that perhaps this difference might be reflected in the fungal population of the two soils. The soil under R. Pseudo-Acacia was found to be loosely packed, moist and to have a pH 6.89-7.00 for both soil and overlying humus. The mosaic pattern of the trees did not seem sufficiently dense to limit significantly the amount of light reaching the ground line. Therefore it was conjectured that the sparse vegetation under the tree was due to the presence of some antagonistic substance that was either exuded from the roots or leached out of the fallen leaves. This contention that limited growth was not due to environmental conditions was substantiated by the comparison of soil conditions of the neighboring stand with that of R. Pseudo-Acacia, and from the results obtained by growing seedlings of Ulmus americana and R. Pseudo-Acacia in crocks containing soil from either their own stand or from the other stand
