These
cotyledons soon became plainly bowed towards the blackened side, evidently
owing to the grease on this side having checked their growth, whilst growth
continued on the opposite side. But it deserves notice that the curvature
differed from that caused by light, which ultimately becomes abrupt near
the ground. These seedlings did not afterwards die, but were much injured
and grew badly.
LOCALISED SENSITIVENESS TO LIGHT, AND ITS TRANSMITTED EFFECTS.
Phalaris Canariensis.--Whilst observing the accuracy with which the
cotyledons of this plant became bent towards the light of a small lamp, we
were impressed with the idea that the uppermost part determined the
direction of the curvature of the lower part. When the cotyledons are
exposed to a lateral light, the upper part bends first, and afterwards the
bending gradually extends down to the base, and, as we shall presently see,
even a little beneath the ground. This holds good with cotyledons from less
than .1 inch (one was observed to act in this manner which was only .03 in
height) to about .5 of an inch in height; but when they have grown to
nearly an inch in height, the basal part, for a length of .
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