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Show 362 MODIFIED CIRCUMNUTATION. CJIAP. VII. experience on full-grown, or nearly full-grown, plants. But the leaflets of young seedlings exhibit a jerking movement at much lower temperatures. A seedling was kept (April1Gth) in a room for half the clay where the temperature was steady at 64° F., and the one leaflet which it bore was continually jerking, but not so rapidly as in the hot-house. Tho pot was taken in the evening into a bod-room where the temperature remained at 62° during nearly the whole night; at 10 and 11P.M. and at 1 A.M. the leaflet was still jerking rapidly; at 3.30 A 111. it was no• seen to jerk, but was observed during only a short time. It was, however, now inclined at a much lower angle than that occupied at 1 A.M. At 6.30 A.M. (temp. 61° F.) its inclination was still less than before, and again loss at 6.45 A.M. ; by 7.40 A.M. it had risen, and at 8.00 A.M. was again soon to jerk. This leaflet, therefore, was moving during tho whole night, and the movement was by jerks up to 1 A.M. (and possibly later) and again at 8.30 AM., though tho temperature was only 61° to 62° F. We must therefore conclude that the lateral leaflets produced by young plants differ somewhat in constitution from those on older plants. In the large genus Dcsmodium by far the greater number of the species are trifoliate; but some are unifoliate, and oven the same plant may bear uni- and trifoliate leaves. In most of the species the lateral leaflets are only a little smaller than tho terminal one. Therefore t.he lateral leaflets of D. gyrans (see former Fig. 148) must be considered as almost rudi· mentary. They are also rudimentary in function, if this expression may be used; for they certainly do not sleep like tho full-sized terminal leaflets. It is, however, possible that tho sinking clown of the leaflets between 1 A.M. and 6.45 A.JII., as above described, may represent sleep. It is well known. that the leaflets go on jerking during tl1e early part of the mght; but my gardener observed (Oct. 13th) a plant in the hot-hou e between 5 and 5.30 A.M., the temperature having been kept up to 82° F., and found that all the leaflets were inclined, but he saw no jerking movement until 6.55 A.M., by which time the terminal leaflet had risen and was a, wake. Two clays after· wards (Oct. 15th) the same plant was observed by him. at 4.47 A.M. (temp. 77° F.), and he fo'?'nd th~t the largo terffil:~l leaflets were awake thou()'h not qmte honzontal; and the 0 Y cause which we cou' ld assoi gn for this anomalous wake f' u1 n ess W. ''I S that the plant had been kept for experimental purposes durmg caAP. vn. SLEEP OF LEAVES. 363 the previous day at an unusually high temperature; the little lateral leaflets were also jerking at this hour, but whether there was any connection between this latter fact and the subhorizontal position of the terminal leaflets we do not know. Anyhow, it is certain that the lateral Jeafiots do not sleep like the terminal leaflets; and in so far they may be said to be in a functionally rudimentary condition. They are in a similar condition in relation to irritability; for if a plant be shaken or syringed, the terminal leaflets sink down to about 45° beneath the horizon; but we could never detect any effect thus produced on the lateral leaflets; yet we are not prepared t~ assert positively that rubbing or pricking the pulvinus produces no effect. As in the case of most rudimentary organs, the leaflets are variable in size; they often depart from their normal position and do not stand opposite one another; and one of the two is frequently absent. This absence appeared in some, but not in all the cases, to be clue to the leaflet having become completely confluent with the main petiole, as might be inferred from the presence of a slight ridge along its upper margin, and from the course of the vessels. In one instance there was a vestige of t?e leaflet, in the shape of a minute point, at the further end of tho ndge. The frequent, sudden, and complete disappearance of one or both of the rudimentary leaflets is a rather sino·ular fact· but it is a much more surprising one that tho leaves ~hich a1·e' first developed on seedling plants are not p11ovided with them. Thus, on one seedling the seventh leaf above tho cotyledons was the first which bore any lateral leaflets, and then only a single one. On another seedling, the eleventh leaf first bore a leaflet· of the nine succeeding leaves five boro a single lateral leaflet, and four bore none at all; at last a leaf, tho twenty-first above the cotyledons, was provided with two rudimentary lateral leaflets. ~rom a widespread analogy in the animal kingdom, it might ave been expected that these rudimentary leaflets would have been better developed and more rt~gularly present on very young !than on older plants. But bearing in mind firstly that lono·ost h ' ' o t"· c aracters sometimes reappear late in life and secondly lllit th . ' ' e specws of Desmodium are generally trifoliate, but that ~ome are unifoliatc, the suspicion arises that D. ,qyrans is freosmc eandte d· ~f rro m a unifoliate species, and that this was descended littl 1 rl 0 late one; for in this case both the absence of tho e ateral leaflets on very young seedlings, and their sub- |