OCR Text |
Show I 368 MODIFIED CIRCUMNUT ATION. CUAP. VII. ..Apios tuberosa (Tribe 8).-The leaflets sink vertically down at night. Phaseolus vttlya1·is (Tribe 8).-The leaflets likowi e sink vertically down at night. In the greenhou. e the petiole of a young leaf rose 16°, and that of an older leaf 10° at night. With plants growing out of doors the leaflets apparently do not sleep until somewhat late in tho season, for on the nights of Julyllth and 12th none of them were asleep; whereas on the night of August 15th the same plants had most of thdr leaflets vcrti· cally dependent and asleep. With Ph. camcalla and J/ernandesii, tho primary unifoliate leaves and the leaflets of the secondary trifoliate leaves sink vertically down at night. 'fhiR holds good with the secondary trifoliate loaves of Ph. Jlo:cburghii, but it is remarkable that the primary unifoliate lo.we, which are much elongated, rise at night from about 20° to about 60° above the horizon. "With older seedlings, however, having the secondary leaves just developed, tho primary leaves stand in the middle of the day horizontally, or are deflected a little beneath the horizon. In one such case tho primary leaves rose from 26° beneath the horizon at noon, to 20° above it at 10 P.M.; whilst at this same hour tho leaflets of the secondary leaves were vertically dependent. Here, then, we have the extraordinary case of the primary and secondary leaves on the same plant moving at the same time in opposite directions. We have now seen that the leaflets in tho six genera of Phaseolero observed by us (with the exception of the primary leaves of Phaseolus Roxburyhii) all sleep in the same manner, na~ely, by sinking vertically down. The movements of the petwl~s were observed in only three of these genera. They rose m Centrosema and Phaseolus, and sunk in Amphicarproa. . Sophora chrysophylla (Tribe 10).-The leaflets rise at rught, and are at the same time dh·ected towards the apex of the leaf, as in Mimosa pudica. . . fl•t Cresalpinia, Ilremato:rylon, Gleditschia, Powcwna.-The lea ~ of two species of Crosalpinia (Tribe 13) rose at night. With Ilrematoxylon Campechianum (Tribe 13) the leaflets move for· wards at night so that their midribs stand parallel to the petiole, and th~ir now vertical lower surfaces are tur~ed ?u~~ wards (Fig. 153). The petiole sinks a little. In Gled~~sch~a,. 1 we understand correctly Duchartre' s d escn.p t·w n, and Ill Pol1l· CHAP. VII . SLEEP OF LEA YES. 369 ciana Gilliesii (both belonging to Tribe 13), the leaves behave in the same manner. Fig. 153. A. B. Hrematoxylon Campechianwn: A, branch during daytime; B, branch with leaves asleep, reduced to two-thirds of natural scale. . CaRsia (Tribe 14).-Tho nyctitropic movements of the leaves m many species in this genus are closely alike, and are highly complex. They were first briefly described by Linnrous, and since by Duchartre. Our observations we1·e made chiefly on a. jloribunda • and corymbosa, but several other species were casually observed. The horizontally extended leaflets sink clown vertically at night; but not simply, as in so many other genera, for each leaflet rotates on its own axis, so that its lower surface faces outwards. The upper surfaces of the opposite leaflets are thus brought into contact with one another beneath the petiole :lllitd sar e well protected (Fig. 154). The rotation and other move~ are effected by means of a well-developed pulvinus at the of each leaflet, as could be plainly seen when a straio-ht ;:ow black_ line had b~en painte~ al?ng it during the d~y. . two ternunalleafl.ets m the daytime mclude rather less than &right angle; but their divergence increases greatly whilst they th:t I am informed by Mr. Dyer a ft ~r. Bentham believes that Fh~u :o ribunda. (a common greenbush) Js a hybrid raised in ce, and that it comes very near to C. lmv'igata. It is no donht the same as the form described by Lindley (' Bot. Reg.,' Tab. 1422) as C. HerberUana. 2 B |