After another
interval, the plant, with 9 leaves pinned out, was again exposed for 1 h.,
the temperature on the ground being again -4o C. Six of the leaves were
killed, and one which did not at first appear injured afterwards became
streaked with brown. The trailing branches, which rested on the frozen
ground, had one-half or three-quarters of their leaves killed, but of the
many other leaves on the plant, which alone could be fairly compared with
the pinned-out ones, none appeared at first sight to have been killed, but
on careful search 12 were found in this state. After another interval, the
plant with 9 leaves pinned out, was exposed for 35 - 40 m. to a clear sky
and to nearly the same, or perhaps a rather lower, temperature (for the
thermometer by an accident had been left on a
[page 293]
sun-dial close by), and 8 of these leaves were killed. Of the free leaves
(those on the trailing branches not being considered), a good many were
killed, but their number, compared with the uninjured ones, was small.
Finally, taking the three trials together, 24 leaves, extended
horizontally, were exposed to the zenith and to unobstructed radiation, and
of these 20 were killed and 1 injured; whilst a relatively very small
proportion of the leaves, which had been allowed to go to sleep with their
leaflets vertically dependent, were killed or injured.
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