On the 24th the pot was again placed on the ground and exposed to a clear sky for between 35 m. and 40 m.  By a mistake the thermometer was left on an adjoining sun-dial 3 feet high, instead of being placed on the grass; it recorded 25o to 26o F. (-3.3o to -3.8o C.), but when looked at after 1 h. had fallen to 22o F. (-5.5o C.); so that the pot was perhaps exposed to rather a lower temperature than on the two first occasions.  Eight leaves had been pinned out, some close to the cork and some above it, and on the following morning five of them (i.e. 63 per cent.) were found killed.  By counting a portion of the leaves we estimated that about 250 had been allowed to go to sleep, and of these about 20 were killed (i.e. only 8 per cent.), and about 30 injured.

Considering these cases, there can be no doubt that the leaves of this Oxalis, when allowed to assume their normal vertically dependent position at night, suffer much less from frost than those (23 in number) which had their upper surfaces exposed to the zenith.

Oxalis carnosa.—­A plant of this Chilian species was exposed for 30 m. to a clear sky, the thermometer on the grass standing at -2o C., with some of its leaves pinned open, and not one leaf on the whole bushy plant was in the least injured.  On the 16th of March another plant was similarly exposed for 30 m., 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., and on two nights afterwards they were again exposed to the same temperature, but this time during 1 h. 30 m.  On neither occasion was a single leaf, whether pinned open or free, injured; and this surprised us much, considering its native tropical African home.  Two plants were next exposed (March 16th) for 30 m. to a clear sky, the temperature of the surrounding grass being now lower, viz., between -3o and -4o C., and all four pinned-open leaves were killed and blackened.  These two plants bore 22 other and free leaves (excluding some very young bud-like ones) and only two of these were killed and three somewhat injured; that is, 23 per cent. were either killed or injured, whereas all four pinned-open leaves were utterly killed.