the cotyledons which had been horizontal
rose up vertically and closed together as when asleep; after thus remaining
on the table for 1 h. 13 m. they began to open. The cotyledons of young
seedlings of another Brazilian species and of C. neglecta, treated in the
same manner, behaved similarly, excepting that they did not rise up quite
so much: they again became horizontal after about an hour.
Here is a more interesting case: seedlings of Cassia tora in two pots,
which had stood for some time on the table in the room just described, had
their cotyledons horizontal. One pot was now exposed for 2 h. to dull
sunshine, and the cotyledons
[page 125]
remained horizontal; it was then brought back to the table, and after 50 m.
the cotyledons had risen 68o above the horizon. The other pot was placed
during the same 2 h. behind a screen in the room, where the light was very
obscure, and the cotyledons rose 63o above the horizon; the pot was then
replaced on the table, and after 50 m. the cotyledons had fallen 33o. These
two pots with seedlings of the same age stood close together, and were
exposed to exactly the same amount of light, yet the cotyledons in the one
pot were rising, whilst those in the other pot were at the same time
sinking.
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