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Show 346 l\10DIFIED CIR UMN TATION. C11Ar. VII. side and afterwards bending to the same side, seemed to us so remarkable, that we endeavoured to discover the cause. Wo imagined that at the commencement of the movement it might be determined by ono of the two halves of the lcn.fiet being a little heavier than the other. Therefore bits of wood were gummed on one side of severn.! leaflets, but this produccu no effect; an<l they continued to twist in the same direction as Fig. 1-1 0. ~~ }; / ~ c. J.felilotus officinrtlis: A, leaf during the d1.1ytime. B, anot~1er l ~af asleet· C, a leaf asleep as viewed from vertically ab<H'C ; but Ill this c~~ :h: terminal leaflet did not happen to be in ~uch close contact Wll lateral one, as is usual. they had previou. ly done. In order to discover whether the same leaflet twisted permanently in tho same cUrection, bl~c: threads were tied to 20 leaves tho terminal leaflets of whl~ twi.s ted so that thei. r upper su' rfaces f ace d wes t , an d 14 wlubte threads to leaflets which twisted to tho cast. Tb 0~ e wder e o'th • served occasionally during 14 days, and they all contmu~ • w~ a single exception, to twist and bend m. the same an·.e e twn '· 10r CHAP. VII. SLEEP OF LEA VBS. 347 one leaflet, which had originally faced cast, was observed after 9 days to face west. The scat of both tho twisting and bending movement is in the pulvinus of the sub-petioles. We believe that the leaflets, especially the two lateral ones, in performing the above described complicated movements generally bend a little downwards ; but we arc not sure of this, for, as far as the main petiole is concerned, its nocturnal movement is largely determined by tho position which the leaf happens to occupy during the day. Thus one main petiole was observed to rise at night 59°, whilst three others ro e only 7° and 9°. The petiolr · and sub-petioles aro continually circumnutating during the whole 24 h., as we shall presently see. The leaves of the following 15 species, llf. officinolis, suaveolens, parvijlora, alba, inf~stu, dentutrt, ,r;racilis, sulcctta., elegun , ca:rule't, petitpil'rreana, mact·orrh iza, ltrd icrt, secwtdijlora, and 'J'a'l.uir;ll, sleep in nearly the same manner as ju t doscrib d; bnt tho bending to one side of the terminal leaflet is apt to fail unl ss the plants are growing vigorously. With .Al. petitpi~rrertna and secundiflora the terminal leaflet was rarely soon to bend to ono side. In young plants of 111. ltalica it bent in tho usual manner, but with old plants in full flower, growing in tho, arne pot and observed at the same hour, viz., 8.30 P.l'II., none of the terminal leaflets on several scores of leaves had bent to one icle, thouO'h they stood vertically; nor had the two lateral leaflets, though standing vertically, moved towards the terminal one. At 1030 P.M., and again one hour after midnight, the terminal leaflets had become very slightly bent to one side, and tho lateral leaflets had moved a very little toward. tho terminal one, so that the position of the leaflets oven at this late hour wa far from the ordinary one. Again, with Jll. J'uurica the terminal leaflets were never seen to bend toward either of tho two lateral leaflets, though these, whilst becoming vertical, had bent towards th~ terminal one. The sub-petiole of the terminal leaflet in this s~ecies is of unusual length, aml if the leaflet had bent to o~e Side, its upper surface could have come into contact only With ~he apex of either lateral leaflet; and tllis, perhaps, is tho m~nmg of the loss of the lateral movement. ~he cotyledons do not sloop at night. The first loaf consists of &Single orbicular leaflet, which twists at night so that the blade stan~ vertically. It is a remarkable fact that with M. 'l'au1·ica, a~d In a somewhat less degree with .Iff. macrorrhizct and petitPierrf! ana, all the many brnall and young leaves produced during |