30 m. and
7 h. 45 m., which sufficed to cause all the other seedlings in the same
pots to become almost rectangularly bent towards the light. They varied in
height from only .04 to 1.15 inch, but the greater number were about .75
inch. Of the 24 cotyledons with their summits thus protected, 3 became much
bent, but not in the direction of the light, and as they did not straighten
themselves through apogeotropism during the following night, either the
caps were too heavy or the plants themselves were in a weak condition; and
these three cases may be excluded. There are left for consideration 21
cotyledons; of these 17 remained all the time quite upright; the other 4
became slightly inclined to the light, but not in a degree comparable with
that of the many free seedlings in the same pots. As the glass-tubes, when
unpainted, did not prevent the cotyledons from becoming greatly bowed, it
cannot be supposed that the caps of very thin tin-foil did so, except
through the exclusion of the light. To prove that the plants had not been
injured, the caps were removed from 6 of the upright seedlings, and these
were exposed before a paraffin lamp for the same length of time as before,
and they now all became greatly curved towards the light.
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