Sean Houtman wrote:

There are a number of cases of an animal producing some chemical
substance that is deleterious to a plant. Many galls are formed by
an insect or other arthropod producing some toxin that the plant
deals with by growing tissue around it, thereby protecting and
feeding the buggie.

I always wonder that crown-gall formation in certain plants can be
regarded as cancer of the plant. Can this growth be included in the
definition of cancer. There is a local tree which produces edible
fruits (Zizyphus species), almost all tree tend to develop tumour-like
growth having a different color from the stem, I don't know whether
eating fruits of such infected plants is harmless for humans for not?


I have not heard of any substance that an animal produces that tends
to produce death in the plant. Since most plants don't hunt down and
eat animals, there isn't any real advantage for animals to produce a
poison that will kill a plant.

Sean