, when the temperature on the grass was only a little lower, viz.,
-3o to -4o C. Six of the leaves had been pinned open, and next morning five
of them were found much browned. The plant was a large one, and none of the
free leaves, which were asleep and depended vertically, were browned,
excepting four very young ones. But three other leaves, though not browned,
were in a rather flaccid condition, and retained their nocturnal position
during the whole of the following day. In this case it was obvious that the
leaves which were exposed horizontally to the zenith suffered most. This
same pot was afterwards exposed for 35 - 40 m. on a slightly colder night,
and every leaf, both the pinned open and the free ones, was killed. It may
be added that two pots of O. corniculata (var. Atro-
[page 289]
purpurea) were exposed for 2 h. and 3 h. to a clear sky with the temp. on
grass -2o C., and none of the leaves, whether free or pinned open, were at
all injured.
Arachis hypogoea.--Some plants in a pot were exposed at night for 30 m. to
a clear sky, the temperature on the surrounding grass being -2o C.
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