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Show :WG l\IODIFlED CIRCUMNU'fA'l'ION. CuAr. VI. a little above the cork. Again, the tips of some few leaflets, which ha<l b en pinnetl close to the cork, projected a little beyon<l the eclg , ·u that the air coulJ circuhttc fr ly round them. This occurred with six leaflets of Oxalis acetosella, ancl their tips certainly ~:>uffered rather less than the rest of tho sttme leaflets; for on the following morning they were still slightly green. 'fhc same result follow cl, even still more dearly, in two cas s with l aflct of Melilotus ~fficinalis which projected a little b yond the cork; and in two other cases some leaflets which were pinned close to the cork were injured, whih;t other free leaflets on the same leaves, which had not space to rotate and assume their proper vertical position, wore not at all injured. Another analogous fact cl erv s notice : we observed on several occasions that a gr -t:ttor number of free leaves were injured on th branehcs which had been kept motionless by some of th 'ir leaves having been pinned to the corks, than on th other branches. 'l'his was conspicuously the ca with thus of Melilot'ltS Petitpierreana, but the injure<l loaves in this instance were not actually ·ounted. vVith Arachis hypogtea, a young plant with 7 stems bor ~ 22 free le<1vos, and of these 5 were injured by the fro:t, all of which were on two stems, bearing four lcnv s pinnecl to the cork· sup! orts. With Oxalis carnosa, 7 fro leaves were injured, and every one of them belonged to a cluster of leaves, some of which had been pinned to the c~rk. vVe could account for the o ca · s only by snpposmg that the branches which w rc quite free had bee:l slightly waved about by th • wind, and that thmr leaves had thus been d little warmed by the sur· rounding warmer air. If we hotel our hamls motion· less before a hot fire and th n wave thorn about, '"0 ' CHAP. VI. SLEEP OF C01'YLEDONS. 297 immediately feel relief; and this is evidently an analogous, though reversed, case. Those several facts -in relation to 1 aves pinn d close to or n little above the cork-supports-to th ir tips proj eting beyond itand to the loaves on branches kept motionless-seem to. ~s curious, as sho,:ving how a <liff'r ·nco, appar ntly tnflmg, may determine tho greater or Joss injury of the leaves. We may even inf r as probable that the less or greater destruction during a frost of the 1 aves on a plant which does not slo p, may often d p nd on the greater or less degree of fl xibility of theil' petioles and of the branches which b ar them. NYcTITROPIC on SLEEP :MovEMENTs OF CoTYLEDONs. We. now c?me .to tho descriptive part of our work, ~nd will begm With cotyledons, pas ing on to leaves m. the n~xt chapter. 'Ve hav met with only two bnef notwes of coty loclons sleopin cr. Hofmeister * after .stating that th cotyledons of ball the observ:d seedlmgs of the Caryophyllcre (AI in re and Sil nero) bend upwards at night (but to what angl he does not state), remarks that those of Stella'ria media rise up so as. to touch one another; they may therefore safely be said to slee~. ~ocondly, according to Harney, t the c~ty!e~ons of M~mosa pudica and of Olianthus Dampten rise up almost vertically at night and approach e~ch other closely. It has been shown in a previous cl apter that the cotyledons of a large number of h ants bend a little upwards at nicrht, and we here ave to meet the diilicult question at what inclination mha!hthey be sai<l to sleep? Accordino- to the view w Ic we m . t . b am am, no movement deserves to be called * ·n· 1 t , lo ehr.e von der Pfl:tnzenzelle,' 1867, p. 327. AdaHFontu,' Murch lOth, 1869. :; II |