plants not only inhibit the seed germination of
other plants but their own as well.
Robert L. Neill and Elroy L. Rice of the university
of Oklahoma involving western ragweed show that it
is inhibitory to nitrogen fixing algae nitrogen
fixing bacteria and nitrifying bacteria.
studies indicated a different pattern of vegetation
around the ragweed and that these patterns are due
neither to mineral nor physical properties of the
soil nor to competition. It is the root exudate,
leaf lechate and decaying leaves of the ragweed that
inhibit many of the early invaders of the abandoned
root exudates from rye grass and wheat seedlings
suppress germination of seeds of field or corn
chamomile, the scentless chamomile or corn mayweed.
Bean seedlings suppress germination of wheat or flax
seeds, Violets suppress germination of wheat seeds.
some plants the suppressing substances may be formed
in the seeds and fruits, in others in the roots,
leaves or stems. Essential oils in many herbs and
even in trees such as poplar, citrus or the
conifers, inhibit the germination of seeds of other
plants to varying degrees.