ÜDS-Fen 2004-1 Soru=75

According to the passage, allelopathic plants —.

The American chestnut was once the most common
canopy tree in the deciduous (non-evergreen)
forests of the eastern United States. It shaded areas
from New England to Georgia until the fungus
Cryphonectria parasitica wiped out the species in
the terrible forest disaster of the early 20th century.
The fungus continues to kill chestnuts before they
can mature. The vacuum left by the chestnut's
destruction is now filled with other species.
Considerable research has gone into understanding
what happened to the American chestnut. But some
scientists remain interested in getting to the root not
of its destruction, but rather of the centuries of
dominance enjoyed by the massive, fragrant and
economically important tree. A team of scientists
recently put forward the idea that the American
chestnut may have been engaged in the chemically
charged competition known as allelopathy. An
allelopathic plant releases potentially toxic
substances into the environment through its roots,
its leaves or processes such as evaporation. Black
walnut, sycamore and sassafras trees are just a few
known allelopaths that limit the germination of
competitor. It's likely that the list will soon branch out
to include chestnut.