The cotyledons of several plants were prepared for trial, but the weather
was mild and we succeeded only in a single instance in having seedlings of
the proper age on nights which were clear and cold. The cotyledons of 6
seedlings of Mimosa pudica were fastened open on cork and were thus exposed
for 1 h. 45 m. to a clear sky, with the temperature on the surrounding
ground at 29o F.; of these, 3 were killed. Two other seedlings, after their
cotyledons had risen up and had closed together, were bent over and
fastened so that they stood horizontally, with the lower surface of one
cotyledon fully exposed to the zenith, and both were killed. Therefore of
the 8 seedlings thus tried 5, or more than half, were killed. Seven other
seedlings with their cotyledons in their normal nocturnal position, viz.,
vertical and closed, were exposed at the same time, and of these only 2
were killed.* Hence it appears, as far as these few trials tell anything,
that the vertical position at night of the cotyledons of Mimosa pudica
protects them to a certain degree from the evil effects of radiation and
cold.
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