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Show 318 1\IODIFIED CIRCUl\INUTATION. CHAP. VII. zenith and to free radiation as when tho blade is horizontal. N evortheloss, in a few instances, loaves which seem to be prevented by their structure from moving to so great an extent as GO" above or beneath the horizon, have been incluuod amongst sleeping plants. It should be premised that the nyctitropic movements of loaves are easily affi cted by the conditions to which the plants have boon subjected. If tho ground is kept too dry, the movom nts are much delayed or fail : according to Da. son,* oven if tho air is very ury the leaves of Impatiens and J\falva are rendered motionless. Carl Knws has also lately insisted t on the great influ n o whi ·h the quantity of water absorbed has on the pcriO<lic movements of leaves; anu he believes that this CttuSO chiefly doter· minos tho variable amount of sinking of tho leaves of Poly_qonum convolvulus at night; and if so, their movements are not in our sens trictly nyctitropic. Plants in order to sleep must have b en exposed to a proper temperature: Erythrina C'tista-galli, out of doors and nailed against a wall, s emed in fairly good. health, but the leaflets did not sl op, whilst those on another plant kept in a warm greenhouse wcr all vertically dependent at night. In a kit hen-garden the leaflets of Phaseolus vulgaris did not sleep dur·jng the early part of the summer. Ch. Royer say ,t referring I suppose to the native plants in :U..,raneo, that they do not sleep when the temperature is below 5° C. or 41° F. In . . f the case of several sle ping plants, vtz., speCies 0 * Dnssen, 'Tijdschrift vor. Nuturlijkf1 G('sch. en Pbysiologi<',' 18::37, vol. i v. p. 1 OG. Seo al!!o Ch. Royer 011 the importance of o. proper stute of turgescence of the eells, in • Anuo.l. dE-.s Sc. Nut. Dot.' (5th series), ix.I868,.p.345· t • Boitrii•"e zur KoutuiSB do~ Bcw<•gungv~,' &o., iu , Flora, 1819, pp. 42, 4R, G7, &eN. t B t, t • Annal. des Se. ~:. 0 • (5th Series), ix. 1868 p.::HiU. CHAP. VII. SLEEP OF LEAVES. 319 Tropreolum, Lupinus, Ipomooa, Abutilon, Siegesbeokia, and probably other genera, it is indispensable that the leaves shoulu be well illuminated during the day in order that they may assume at night a vertical position; and it was probably owing to this cause that seedlings of Chenopodium album and Siegesbeclcia orientalis, raised by us during the midcllc of the wint r, though k.ept at a. pr?per temperature, did not sleep. Lastly~ viOlent ag1tatwn by a strong wind, during a few mmutes, of the leaves of Maranta arundinacea (which previously had not been disturbed in the hothouse), prevented their sleeping durin()' the two next m'gh t s. b We will n?w give our observations on sl eping plants, made m the manner described in the Introduction. The stem of the plant wa always secured (when not stated to the contrary) clos to the base of the leaf, the movements of which were bein()' observed so as t~ prevent the stem from circumnutba ting. As' the tracmgs were made on a vertical glass in front of the plant, it was obviously impos ibl to trace its course a.~ so?n as the loaf became in the evening greatly mclmed either upwards or downwards; it ~ust therefore be understood that the broken line · m the diagrams, which represent the evening and nocturnal courses, ought always to be prolono-od to a much greater distance, either upwards or do~nward. , than appears in them. The conclusions which may b deduced from our observations will be given near tho end of this chapter. In. the following list all the genera which include sleepmg plants arc given, as far as known to us. ~rhe :~me arrangement is followed as in former cases, and e number of the Family is appended. This list possesses some interest, as it shows that the habit of ,., •, " ~ I |
