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Show 290 MODIFIED CIRCUMNUTATION. CIIAl'. VI. anotber night for 1 h., when the tompern.turc of the gms~ was _ 4o c .. and now all the leaves on a largo bnsh, wl1cther pmned flat ope~ or free, were killed, blackened, and shrivelled, w_ith the exception of those on one small branch; low down, whJCh was very slightly protected ~y the lea:e.s on the branches above. Another tall bm;h, with four of Its large compound leaves pinned out horizontally, was aftcr:vards ~xposed (temp. of surrounding grass exactly the same, v1z., - 4 C.), but only for SO m. On the following mornino· every single leaflet on these four leaves was dead, with both their upper and lower surfaces completely blackened. Of the many free leav~s on tho hush, only seven were blackened, and of these only a smgle one (which was a younger and more tender leaf than any of the pinned ones) had both surfn.ces of tho leaflets blackened. ~be contrast in this latter respect was well shown by a free leaf, whJCh stood between two pinned-open ones; for these l~tter ha~ the lower surfaces of their leaflets as black as ink, wh1~st the mte:· mediate free leaf though badly injured, still retamed a plam tinge of green on' the lower surface ~f tl~c leaflets. This bush exhibited in a striking manner the cv1l ef1ccts of the leaves n~t being allowed to assume at night their normal dependent posJ· tion · for had they all boon l)l'Ovcntcd from doing so, assuredly ever~ single leaf on the bush would have been utt~rl~ killed by this exposure of only SO m. The leaves whilst smkmg dowJ~wards in the evening twist round, so thn.t the upper surface 18 turned inwards and is thus better protected than the outwardly turned lower s~u·face. Nevertheless, it was always the upper ~:;urface which was more blackened than the lower, whenr.v~r any difference could be perceived between them; but whether thJs was due to the cells ncar the nppcr surface being more tender, or merely to the.u conta·m ·m g more c hlo rop byll ' we do not kno.w . . . 1 t 'th n1any plants whJC1l MeWotus officmahs.-A argo po Wl ' d had been kept during the winter in the greenhouse, was expose during 5 b. at night to a slight frost and clear sky. Fou~ leaves had been pinned out, and these died after a_ few day~, but so did many of the free leaves. rrhereforo nothmg ,certa]JJ\ could be inferred from thi.s tn.a l, t 11 oug1 ·t. d'cn.ted thattw 1 1 m 1 ' t horizontally extended leaves suffered most. Another la~g~ P;n with many pl~nts was nex_t exposed fo~· 1 h., ~he t~f;r~.ur~en the surroundmg grass bemg lower, VIZ., - S to 'k' for Jmtves had been pinned out., and the result was shtr~ ~n~e'dor on the followm• g mm·m• ng all these wer•e .c nd muc lllJUl 10U CHAP. VI. USE OF SLEEP MOVEMENTS. 291 killed, and n~n? of the _many free leaves on the several plants were at all IDJUred, With tho doubtful exception of two or three very young ones. Melil?tus It~lica.-Six leaves w~re pinned out horizontally, three With thmr upper and three With their lower surfaces turned to the zenith. 'rhe plants were exposed for 5 h. to a clear sky the ~m~erature on ground being about - 1° C. Next mornin~ the SJX pmned-open leaves seemed more injnred even than tbe younger and more tender free ones on the same bnmches. 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 whethe1· the leaves with their upper or those with their lower surfaces turned to the zenith had suffered most. Melilotus suaveolens.-Some plants with 8 leaves pinned out were exp~sed to a cle~r sky during 2 h., the temperature on the surroundmg ~ass bem_g- 2° C. Next morning 6 out of these 8Ieaves were m a flaccid condition. There were about 150 free leaves on the plant, and none of these were injured, except 2 or S very young o~es. But after two days, the plants having been brought back mto the greenhouse, the 6 pinned-out leaves all recovered. Mel~lotu.~ Taurica.-Sevemi plants were exposed for 5 h. during t~o ~ghts to a clear sk! and slight frost, accompanied by some wmd, and 5 leaves which had been pinned out suffered more than those both above and below on tho same branches which ~ad gone to sleep. Another pot, which had likewise been kept 1n the greenhouse, was exposed for S5-40 m. to a clear sky the ~mpera_ture of the surrounding grass being between - so ancl ; 1f d 0• Nme leaves had been pinned out, and all of these were h~e b On the same plants there were 210 free leaves which kill de~n allowed to go to sleep, and of these about SO were e 'I.e. only S8 per cent. Melilotus Petit · . . Th 1 8 for 35 pzt?Hanu.- e Pants were exposed to a clear ~o -:40 m. : temperature on surrounding grass - so to t . ~· SlX leaves had been pinned out so as to stand about T~nc above the cork, and four bad been pinned close to it. su:::Jo leaves were all killed, but the closely pinned ones ret . d most, as 4 of the 6 which stood above the cork stm nu:: small patches of a green colour. A eonsider~bJe much .r'. but not nearly all, of the free leaves, were killed or IDJured, whereas all the pinned out ones were killed. u 2 , ... ; ::~ I ' I .I".' ·'' |