Another large pot with many
plants was next exposed for 1 h., the temperature on the surrounding grass
being lower, viz., -3o to -4o C. Ten leaves had been pinned out, and the
result was striking, for on the following morning all these were found much
injured or
[page 291]
killed, and none of the many free leaves on the several plants were at all
injured, with the doubtful exception of two or three very young ones.
Melilotus Italica.--Six leaves were pinned out horizontally, three with
their upper and three with their lower surfaces turned to the zenith. The
plants were exposed for 5 h. to a clear sky, the temperature on ground
being about -1o C. Next morning the six pinned-open leaves seemed more
injured even than the younger and more tender free ones on the same
branches. The exposure, however, had been too long, for after an interval
of some days many of the free leaves seemed in almost as bad a condition as
the pinned-out ones. It was not possible to decide whether the leaves with
their upper or those with their lower surfaces turned to the zenith had
suffered most.
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