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Show 394 MODIFIED CIRCUMNUTATION. CuA.P. VII. its fellow. The movement of another leaflet, wllon asleep, was traced between 6 P.M. and 10.35 P.M., and it clearly circu. mnutated, for it continued for two homs to sink, thou rose, and then sank still lower than it was at 6 I>.M. It may be seen in the preceding figure (167) that tho leaftot, when the plant was subjected to a rather low temperature in the house, descended and ascended during the middle of the day in a somewhat zigzag line; but when kept in tho hot-house from 9 A.M. to 3 P.M. at a high but varying temperature (viz., between 72° and 83° F.) a leaflet (with the petiole secured) circurnnutated rapidly, for it made three largo vertical ellipses in tho course of the six hours. According to Brongniart, ll!farsi!ea p~tbescens sleeps like the present species. These plants are the sole cryptogamic one~ known to sleep. Summary and Concluding R emarks on the Nyctitropic or Sleep-movements of Leaves.-That those movements are in some manner of high importance to the plants which exhibit them, few will dispute who have ob· served how complex they sometimes arc. Thus with Cassia, the leaflets which are horizontal during the day not only bend at night vertically downwards with the terminal pair directed considerably backwards, but they also rotate on their own axes, so that their lower surfaces are turned outwards. The terminal leaflet of Melilotus likewise rotates, by which movement one of its lateral edcres is directed upwards, and at the same time it mo~~s either to the loft or to the right, until its upper surface comes into contact with th~t of the lateral leaflet on the same side, which has hlre· wise rotated .on its own axis. With Arachis, all four leaflets form together during the night a sin~le vertical packet ; and to effect this the two anter~or leaflets have to move upwards and the two postenor ones forwards, besides all twisting on their own axes. In the genus Sida the leaves of some speC·i es mov eat night through an angle of 90° upwards, and of others CHAr. VII. SUMMARY ON SL:EEP OF LEAVES. 305 through the same angle downwards. vVe have seen a. similar difference in tho nyctitropic movements of tho cotyledons in the genus Oxalis. In Lupinus, again, the leaflets move either upwards or downwards; and in some species, for instance L. luteus, those on one side of the star-shaped leaf move up, and those on the opposite side move down ; the intermediate ones rotating on their axes; and by those varied movements, the whole leaf forms at night a vertical star instead of a horP'lontal one, as during the day. Some leaves and leaflets, besides moving either upwards or downwards, become more or loss folded at night, as in Bauhinia and in some species of Oxalis. The positions, indeed, which leaves occupy when asleep are almost infinitely diversified; they may point either vertically upwards or downwards, or, in the case of leaflets, towards the apex or towards the base of the leaf, or in any intermediate position. They often rotate at least as much as 90° on their own axes. Tho leaves which arise from upright and from horizontal or much inclined branches on the same plant, move in some few cases in a different manner, as with Porlioria and Strephium. rrhe whole appearance of many plants is wonderfully c~anged at night, as may bo seen with Oxalis, and st1ll more plainly with Mimosa. A bush of Acacia Farnesiana appears at nio·ht as if covered with little dangling bits of string in~tead of leaves. Excluding a fe.w genera not seen by ourselves, about which we are.m doubt, and excluding a few others the leaflets of wh1eh rotate at night, and do not rise or sink much, there are 37 genera in which the leaves or leaflets rise, often moving at the same time towards the apex or towar~s the base of the leaf, and 32 genera in which they smk at night. The nyctitropic movements of leaves, leaflets, and |
