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Show 288 MODIFIED OIROUMNUTATION. CHAP. VI. and in the morning two of them were dead, whilst not a single other leaf on tho many plants was oven injured. On the 23rd the pot was exposed for 1 h. 30m., tho temperature on the grass being only - 2° 0., and not one leaf w118 injured: the pinned open leaves, however, all stood from ~ to ~· of an inch above the cork. On tho 24th the pot was again placed on the ground ancl exposed to a clear sky for between 35 m. and 40 m. Dy a mistake tho thermometer was loft on an adjoining sun-dial 3 feet high, instead of being placed on the graRs; it recorded 25° to 26° F. (- 3·3° to - 3·~° C.), but when looked at after 1 h. had fallen to 22° F. (- 5'5° C.); so that tho pot was perhaps exposed to rather a lower temperature than on the two first occasions. Eight leaves had been pinned out, some close to tho cork and some above it, and on the following morning five of them (i.e. 63 per ceut.) were found killed. By counting a portion of the leaves we estimated that about 250 bad 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 bo no doubt that tho 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 surfaceB exposed to the zenith. Oxalis carnosa.-A. plant of this Chilian species was exposed for 30m. to a clear sky, the thermometer on the grass standing at- 2° C, with some of its leaves pinned open, and not one leaf on the whole bushy plant was in tho least injured. On tho 16th of March another plant was similarly exposed for 30m., when the temperature on the grass was only a little lower, viz., - 3° to - 4 ° 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 exposedhori· zontally 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 0. coru'iculata (var. Atro· CHAP. VI. USE OF SLEEP MOVEMENTS. purpurea) were exposed for 2 h. and 3 11 · t o a c1 c ar s k y w1.t h th temp. on grass - 2° C and none of the 1 ' e pinned open, were at ~II injured. caves, whether free or .J.rachis hypogrea.-Some plants in t for 30m. to a clear sky the temp ~ ro. were exposed at night grass being- 2o c and; t . 1 eia me on the surrounding ., n wo mg tts afterwards tb . exposed to the same temperature but th' t', d ~ywercagmn On neither occasion was a siogl~ lc f I\ 1~e u~·mg 1 h. 30m. free, injured; and this sur ris d a ' ~ e e~· PI~ed open or tropical African home. T~o e la~~s ~lC:l, considcrmg its native 16th)for30m. to a clear sky, tl;e tern e:I: ~:xt oxposctl (March grass being now lower viz b t p a ~ue of the surromHhng £ . ' ., e ween - vo and 4o C d our pmned-open leaves wore kill d d bl - ., an all plants bore 22 other and free 1 cave: a~ ~clcened. These two bud-like ones) and only two of tl . (cxc.lud~ng some very young what injured. that is 23 . lOSe wmo ~nlled and three somewhereas all f;ur pinn~d o:ei lcent. were mthcr killed or injured, On another night two e~ ea.ves were utterly killed. for between 35m. and 40 po \with several plants were exposed r~ther lower temperature,~r ~ ~h cl.Qar sky,. and pcr~aps to a lugh, close by stood at - 3·3o to _e~~~metcr on a dial, 3 fee~ leaves were pinned 0 )en C. In one pot th1·ee 44 free leaves 26 w 1 .' ~nd all were badly injUl'cd . of the ' ere InJnred th t · 59 ' other pot 3 leaves were . , a lS, per cent. In tho ot~er leaves were prevcn~~~ntd op~n a~d all were killed; four stiff paper gummed across t 10m s cepmg by ~arrow strips of leaves, 10 were killed 2 hem? ~nd all wero Jnllod; of 24 frco 50 per cent. of the fr~e lmuch IDJured? and 12 unhurt; that is, jured. Taking the t e~ves were either killed or much inmore than half of the wfo plo s togetb~r, we may say that rather k'll d . . ree eaves whwh w . 1 . I e or lllJured whilst all tl t' . eir as eep, were either which had been ~rcvent d f w e~ horizontally extended leaves or much injured. e rom gomg to sleol), Wel·o either Jcille~l Cassia jloribunda -A b a clear sky, the t~m . us~ was exposed at night for 40 m. to -20 c., and not a l reratu~e. on the smrounding grass beinoea was IDJured.* It was again exposed o~ • 0Msia l8J • to a clear sk mpata was exposed calliantha (a[. ~r 35 m., anu 0. 00 m., the te~Iana species) for surround· perat.ut·e on the and n .;hng grass being _ 2o 0 E:l er were in the Jea~t i~jurecl. But when 0. ltevigata "as t•xposed for l h tb t. 0 tl ., e em}J. b n lll surrountling gmss being ·tween -go and- 4o 0 leaf wa~; killed. ., every u ,, ,1",1 II |