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Show 410 MODIFIED CIRCUl\iNUTATIO:N. CHAP. VII. case of a sleeping leaf, we see that it makes a single ellipse in t.he twenty-four hours, which resembles one described by a non-sleeping leaf in every respect, except that it is much larger. In both cases tho course pursued is often zigzag. As all non-sleeping leaves are incessantly circumnutating, we must conclude that a part at least of the upward and downward movement of one that sleeps, is due to ordinary circumnutation; and it seems altogether gratuitous to rank tho remainder of the movement under a wholly different head. With a multitude of climbing plants the ellipses which they describe have been greatly increased for another pur· pose, namely, catching hold of a support. vVith these climbing plants, the various circumnutating organshaYe been so far modified in relation to light that, differently from all ordinary plants, they clo not bond towanls it. With sleeping plants the rate and amplitude of tho movements of the leayes have been so far mo(lifiecl in relation to light, that they move in a certain direction with the waning light of the evening ancl with the increasing light of the morning more rapiclly, and to a greater extent, than at other hours, . But the leaves and cotyledons of many non-slcepr~g plants move in a much more complex manner thanm the cases just alluded to, for they describe two, th~·ee, or more ellipses in the course of a day. Now, 1f a plant of this kind were converted into one that slept, one s1. de of one of t h c sev. era1 e1 11· psos wb ich each leaf daily describes, would have to be greatly incrca ed in length in the evening, until the l e~f stood ver· tically when it would o·o on circumnntatmg about the same s' pot. On the fbo llow.m g mornm· g., t l1 ~ sr' de odf .a nother e l h.p sc wou lcl h ave t o b e si. in i·lw·' rly• mc. rease. in length, so as to brm. g the l ea f b ack. ag. am mto Jttes diurnal position, when it would agam cncumnuta CHAP. VII. SUMMARY ON SLEEP OF LEAVES. 411 until the evening. If the reader will look, for instance, at the diagram (Fig. 142, p. 351), representing the nyctitropic movements of the terminal leaflet of T1'ijolium subterraneum, remembering that the curved broken lines at the top ought to be prolonged much higher up, he will see that the great rise in the evening and the great fall in the morning toget~er form a large ellipse like one of those described during the daytime, differing only in size. Or, he may look at the diagram (Fig. 103, p. 236) of the 3! ellipses described in the course of 6 h. 35 m. by a leaf of Lupinus speciosus, which is one of the species in this genus that does not sleep ; and he will see that by merely prolonging upwards the line which was already rising late in the evening, and bringing it down again next morning, the diagram would repTesent the movements of a sleeping plant. With those· sleeping plants which describe several ellipses in the daytime, and which travel in a strongly zigzag line, often making in their course minute loops, ~angles, &c., if as soon as one of the ellipses begins m the evening to be greatly increased in size, dots are ~ade every 2 or 3 minutes and these are joined, the !me then described is almost strictly rectilinear, in s~rong contrast with the lines made during the daytl~ e. This was observed with Desmodium gyrans and ~tmasa pudica. With this latter plant, moreover, the pmnre converge in the evening by a steady movement, ~hereas during the clay they arc continually convergmg and diverging to a slight extent. In all s~ch cases it was scarcely possible to observe the ~Iffere~ce in the movement during the day and evenmg, Without being convinced that in the evening the plant saves the expenditure of force by not moving ~t€rally, and that its whole energy is now expended |
