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Show 316 MODIFIED CIRCUMNUTATION. CHAP. VI. f T :.t. z·um strictum, in combination with that led on o r2 J 0 2 • _, 1· 'b · · of t h e fi rs t t r.u e leaf· Lastly' the w1ue .c 1stn ut10n m the dicotyledonous series of plants with cotyledons whw. h s1 e ep. ReflectinOb ' on thes sever. al fa. cts, our cone 1u s.w n see ms J. ustified ' that the nyct1tro. p1C ml ove-ments of co t Yl edons ' by which the bla.u e 1s mace _t,o stand e1' the r, ve,·tically or almost vcrtwally upwarus L • 1 or d ownwar d s at niOb 'ht ' has been acqmred, at east . t cases for some special purpose ; nor can we m mos ' · f 1 doubt that this purpose is the prote~twn o t le upper surf ace of the blade ' and perha. ps of the central bud or plumule, from rauiation at mght. CnAr. VII. MODIFIED OIROUl\'INUTATION. 317 CHAPTER VII. MODIFIED CIROUMNUTATION: NYOTI'rROPIO OR SLEEP MOVEMENTS OF LEAVES. Conditions nrcessary for these mnvemon ts-- Li t of Genera anu F amilie1-1, which include sleeping plants-Description of the movements in the several GcneJa- Oxo.lis : leafl ts foldod at night-Averrhoo.: rapid movements of the leatlds-Porlieria : leaflets close when pl11nt kept very dry-Troproolum: leuveH do not sleep uule s wt:ll illuminated during dny-Lupinus : various modes of slec pingMelilotus: singular movements of terminfll lcaflet - 1'dfoliumDesmodium: rudimentary b.tcral leaflets, movements of, not dt·· veloped on young plants. state of their pulvini-Cus~; io.: complex movements uf the leaflets-Bauhinia : leaves folued at nightMimosa pudica: compounded movements of leaves, effect of darkness- Mimosa albida, reduced leaflets of- Scbrankia : downward movement of the pinnre-Marsilea : the only cryptogam known to sleep-Concluding remarks and summary- Nyctitropism consists of modified chcumnutation, regulated by the alternations of light and darkness-Shape of first true leaves. WE now come to the nyctitropic or sleep movements of leaves. It should be remembered that we confine this term to leaves which place their blades at night either in a vertical position or not more than 30° from the vertical,-that is, at least 60° above or beneath the horizon. In some few cases this is effected by the rotation of the blade, the petiole not being either raised or lowered to any considerable extent. The limit of 30° from the vertical is obvionsly an arbitrary one, and has been selected for reasons previously assigned, namely, that when the blade approaches the perpendicular as nearly as this, only half as much of the surface is exposed at night to the I. ~r l·f.~'' 1 .•. · ~ '!~ :j ,,t.:l |