that more dew had congealed into hoar-frost on the closely pinned leaflets, than on those which stood horizontally [page 296] a little above the cork.  Again, the tips of some few leaflets, which had been pinned close to the cork, projected a little beyond the edge, so that the air could circulate freely round them.  This occurred with six leaflets of Oxalis acetosella, and their tips certainly suffered rather less then the rest of the same leaflets; for on the following morning they were still slightly green.  The same result followed, even still more clearly, in two cases with leaflets of Melilotus officinalis which projected a little beyond the cork; and in two other cases some leaflets which were pinned close to the cork were injured, whilst other free leaflets on the same leaves, which had not space to rotate and assume their proper vertical position, were not at all injured.

Another analogous fact deserves notice:  we observed on several occasions that a greater number of free leaves were injured on the branches which had been kept motionless by some of their leaves having been pinned to the corks, than on the other branches.  This was conspicuously the case with those of Melilotus Petitpierreana, but the injured leaves in this instance were not actually counted.  With Arachis hypogaea, a young plant with 7 stems bore 22 free leaves, and of these 5 were injured by the frost, all of which were on two stems, bearing four leaves pinned to the cork-supports.  With Oxalis carnosa, 7 free leaves were injured, and every one of them belonged to a cluster of leaves, some of which had been pinned to the cork.  We could account for these cases only by supposing that the branches which were quite free had been slightly waved about by the wind, and that their leaves had thus been a little warmed by the surrounding warmer air.  If we hold our hands motionless before a hot fire, and then wave them about, we [page 297] immediately feel relief; and this is evidently an analogous, though reversed, case.  These several facts—­in relation to leaves pinned close to or a little above the cork-supports—­to their tips projecting beyond it—­ and to the leaves on branches kept motionless—­seem to us curious, as showing how a difference, apparently trifling, may determine the greater or less injury of the leaves.  We may even infer as probable that the less or greater destruction during a frost of the leaves on a plant which does not sleep, may often depend on the greater or less degree of flexibility of their petioles and of the branches which bear them.

Nyctitropic or sleep movements of cotyledons.