This holds good with
species the cotyledons of which rise or sink so much at night that they may
be said to sleep, as well as with others which rise only a little. But
different species are affected in very different degrees by changes in the
light.
[page 124]
[For instance, the cotyledons of Beta vulgaris, Solanum lycopersicum,
Cerinthe major, and Lupinus luteus, when placed in darkness, moved down
during the afternoon and early night, instead of rising as they would have
done if they had been exposed to the light. All the individuals of the
Solanum did not behave in the same manner, for the cotyledons of one
circumnutated about the same spot between 2.30 and 10 P.M. The cotyledons
of a seedling of Oxalis corniculata, which was feebly illuminated from
above, moved downwards during the first morning in the normal manner, but
on the second morning it moved upwards. The cotyledons of Lotus Jacoboeus
were not affected by 4 h. of complete darkness, but when placed under a
double skylight and thus feebly illuminated, they quite lost their
periodical movements on the third morning.
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