, every leaf was killed.
[page 290]
another night for 1 h., when the temperature of the grass was -4o C.; and
now all the leaves on a large bush, whether pinned flat open or free, were
killed, blackened, and shrivelled, with the exception of those on one small
branch, low down, which was very slightly protected by the leaves on the
branches above. Another tall bush, with four of its large compound leaves
pinned out horizontally, was afterwards exposed (temp. of surrounding grass
exactly the same, viz., -4o C.), but only for 30 m. On the following
morning every single leaflet on these four leaves was dead, with both their
upper and lower surfaces completely blackened. Of the many free leaves on
the bush, only seven were blackened, and of these only a single one (which
was a younger and more tender leaf than any of the pinned ones) had both
surfaces of the leaflets blackened. The contrast in this latter respect was
well shown by a free leaf, which stood between two pinned-open ones; for
these latter had the lower surfaces of their leaflets as black as ink,
whilst the intermediate free leaf, though badly injured, still retained a
plain tinge of green on the lower surface of the leaflets.
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