Phototropism is the movement plant
structures in response light.
Phototropism may bepositive .
Positive phototropism is that
which the plant movement (
growth) is towards the source and
negative phototropism that in which
the (or growth) is inverse,
from the light source.

relates to auxins since
exposition of one side the plant to
light these hormones
concentrate in darker side. This fact
the auxin action upon stem
to be positive, .e., the growth of the
side is more intense the
plant arcs towards lighter side. In
the (when submitted to light,
general experimentally) the auxin
is negative (over the range),
the growth of darker side is
inhibited the root curves towards
side.