greatly arched towards the light, became straight and strictly parallel
with the surface of the soil in the pots; the basal part being now
rectangularly bent. All this great amount of curvature, together with the
subsequent straightening of the upper part, was often effected in a few
hours.
[After the uppermost part has become bowed a little to the light, its
overhanging weight must tend to increase the curvature of the lower part;
but any such effect was shown in several ways to be quite insignificant.
When little caps of tin-foil (hereafter to be described) were placed on the
summits of the cotyledons, though this must have added considerably to
their weight, the rate or amount of bending was not thus increased. But the
best evidence was afforded by placing pots with seedlings of Phalaris
before a lamp in such a position, that the cotyledons were horizontally
extended and projected at right angles to the line of light. In the course
of 5 ? h. they were directed towards the light with their bases bent at
right angles; and this abrupt
[page 470]
curvature could not have been aided in the least by the weight of the upper
part, which acted at right angles to the plane of curvature.
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