The Antibiotic Effects of Plants in Laboratory and Field

In laboratory experiments, plant extracts of small everlasting (Antennaria microphylla Rydb.), field pussytoes (A. neglecta Greene), and leafy spurge (Euphorbia esula L.) were toxic to germinating seeds. Extracts of small everlasting inhibited vegetative development of leafy spurge, and soil taken from the immediate vicinity of roots inhibited germination and radicle elongation of germinating seeds of some species. Small everlasting competes vigorously with leafy spurge, and this competition cannot be attributed to morphology and growth habit. It suppressed vegetative growth of leafy spurge from rhizome sections in which the two species were competing in pots. In field experiments, this shallow-rooted, lowgrowing plant exhibited a marked inhibition on the growth of the vigorous, deep-rooted perennial, leafy spurge, as did the soil in which small everlasting had been growing. Antibiotic competition appears to be significant with the Antennaria spp., and the paucity of forbs in patches of leafy spurge, even when bare ground is visible between shoots, suggests that this species also exerts antibiotic effects on other plants. Allelopathy is probably a significant influence in interspacial relationships of species in most plant communities. A fuller knowledge of these relationships and their causes could lead to the utilization of this phenomenon in weed control.