GERMINATING SEED

Many plants not only inhibit the seed germination of other plants but their own as well.  Experiments by 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.

Field 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 fields.

The 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.

In 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.