| OCR Text |
Show 404 MODIFIED CIRCUMNUTATION. CHAP. YII. single large ellipse is described during each twenty-four hours. Such ellipses are generally narrow and vertically directed, for the amount of lateral movement is small. That there is some lateral movement is shown by the ascending and descending lines not coinciding, and occasionally, as with Desmodiurn gy'mns and 'l'hah'a dealbata, it was strongly marked. In tho case of Malilotus the ellipses described by the terminal leaflet during the day are laterally oxtondod, instead of vertically, as is usual ; and this fact evidently stands in relation with the terminal leaflet moving laterally when it goes to sleep. With the majority of sleeping plants the leaves oscillate more than once up and down in the twenty-four hours; so that frequently two ellipses, one of moderate size, and one of very largo.size which includes the nocturnal movement, are clcscnbecl within the twenty-four hours. For instance, ft loaf which stands vertically up clnring the night will si~k in the morning, then rise considerably, again sink m the afternoon, and in tho evening reascend and ass~mo its vertical nocturnal position. It will thus c~escnbe, in the course of the twenty-four hours, two oll1pscs of unequal sizes. Other plants describe with~n tho same time, three, four, or five ellipses. Occas~ona!l~ tho longer axes of the several ellipses extend m tbflcront directions of which Acacia Farnesiana offered a good instance. ' The following cases will give an idea of the rate of movement: Oxalis acetosella complotc<l ~wo ellipses at the rate of 1 h. 25 m. for each; J,!a?'szlea quadri-foliata at the rate of 2 h.; Tr1jolium s'uUtm-rwwum, one in' J3' h. 3' 0m.· and Arach2·s hypogtea, m· 41 1 50 m. • . But the number o' f ellipses <loscn·b od w·it hm' a gl YOn ti. me depends largely on t h e s t a t e of tho pl·.a nt and_ on the conditions to which it is exposed. It oft~n hap pens thai a single ellipse may b e d escn'b ed dunng one CHAP. VII. SUMMARY ON SLEEP OF LEAVES. 405 day, and two on the next. Erythrina corallodendron made four ellipses on tho first clay of observation and only a single one on tho third, apparently owing to having been kept not sufficiently illuminated and perhaps not warm enough. But there seems likewise to be an innate tendency in different species of the same genus to make a different number of ellipses in the twenty-four hours: tho leaflets of Trijoliun2 repens made only one; those of T. resupinatum two, and those of T. subterraneum three in this time. Again, the leaflets of Oxulis Plumierii made a single ellipse ; those of 0. bupleurifolia, two; those of 0. Jl aldiviana, two or three; and those of 0. acetosella, at least :five in the twenty-four hours. The line followed by the apex of a leaf or leaflet, whilst describjng one or more ellipses during the day, is often zigzag, either throughout its whole course or only during the morning or evening: Robinia offArecl an instance of zigzagging confined to the morning, and a similar movement in the evenino· is shown in the diagram (Fig. 126) given under Sida.b The amount of.the zigzag movement depends largely on the plant bemg placed under highly favourable conditions. But even under such favourable conditions, if the dots which mark the position of the apex arc made at considerable intervals of time, and tho dots are then joined, t~e course pursued will still appear comparatively ~Imple, although the number of the ellipses will be m~reased; but if dots are made every two or three mmutes and these are joined, the result often is that :1~ the lines are strongly zigzag, many small loops, rian?les, and other :figures being also formed. This f~ct Is shown in two parts of tho diagram (Fig.150) 0 t~e movements of Desmodium gyrans. Strephium flonbundum, observed un<lor a high temperature, |
