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Show 260 CIRCU MNUTA TION OF LEAVES. CHAP. IV. . . and ymnospermous Dicotyledons amongst ordmar y t lg dons together with several and amongs t Monaco Y. eb een ' described. It wou ld ' 0 . t ms have now h ,. rr ryp oga ' e rash to assume that t e grm\lnb therefore, not b . . mnutate as we have seen f ll l)lants cucu ' 'Th leaves o a l is the case with cotyledons. e reason to concluc e enerally lies in the petiole, but seat o.f moveme~t ~he 1ctiolc and blade, or in the sometimes both In t If tho movement differed much blade alone. The e~t~ut o the dista,nce passed over was in different plants' 'tl Pistia which ought perhaps t except WI 1 never grea' . d d amongst' sleeping plants. 'I'h e to have been mclu ~ tho leaves was only occasionally angular mo:rement o varied from only 2o (and pro· measured ; It cm~.Imonl y instances) to about lOo; but bably even less m some be"n The move· 23o . the common u. • • it amo. unhte' df l to . a vmer ti.C a1 p 1a nc, 1-ut as the ascendmg u ( mentIS c Ie · Y m1 · ever coi.n CI<. l c( l ' there was alw. ays and descendmg mes n d thus irregular elhpses some lateral movement, an t therefore deserves to were forme d . rrhe movement ' ' . for all' cu. cumnu t a· f · . nuta 1011, < be called one o cucum . ll' - tha,t is ()'rowth d t descnbe e Ipses, ' b ting organs ten o rowth on nearly but not on one side is s:ICce~ded ~r ~ clli Jses, or the zigzag quite the opposite side. Ih ll.I cs are generally · o- drawn-out c 1P8 ' . lines representmb . L ll'. their mmor axes t 'tl the Came u1, very narrow; ye WI l . h tb Eucalyptus more than were half as long, .and ':I~ r e In the case of Cissus, half as long as theu maJor axes. ltcd circles than ·t of the figure more ncar- ly. rel)resCI t .. therefore par s 1 . 1 movcmcn 1s ellipses. The amount of at rn. . the lonaer axes . d bl Moreover, b sometimes consl era e. . vith the Bean, · 1 f d elhrJscs (as ' of the successive y orme . . l instances tl1e Cissus, and Sea-k a l e ) ' an d In. se.v ewrae re extended I·n zin·zag lines representing cll.Ipse{h same day or on ~c~·y different directions durmg e CHAP. IV. CIRCUl\1NUTATION OF LEAVES. 261 the next day. The course followed was curvilinear or straiaht, or slightly or strongly zigzag, and little loops or trhtngles were often formed. A single large irregular ellipse may be described on one day, and two smaller ones by the same plant on the next clay. With Drosera two, and with Lupinus, Eucalyptus and Pancratium, several were formed each day. ~rhe oscillatory and jerking movements of the leaves of Dionrea, which resemble those of the hypocotyl of the cabbage, are highly remarkable, as seen under the microscope. ~rhey continue night and day for somo months, and are displayed by young unexpancled leaves, and by old ones which have lost their sensibility to a touch, but which, after absorbing animal matter, close their lobes. We shall hereafter meet with the same kind of movement in the joints of certain Gramincro, and it is probably common to many plants while circumnutating. It is, therefore, a strange fact that no such movement could be detected in the tentacles of Drosera rotundijolia, though a member of the same family with Dionroa ; yet the tentacle which was observed was so sensitive, that it began to curl inwards in 23 seconds after being touched by a bit of raw meat. One of the most interesting facts with respect to the circumnutation of leaves is the periodicity of their movements; for they often, or even generally, rise a little in the evening and early part of the night, and sink again on the following morning. Exactly the same phenomenon was observed in the case of cotyledons. The leaves in 16 genera out of the 33 which were observed behaved in this manner, as did probably ~others. Nor must it be supposed that in the remainIng 15 genera there was no periodicity in their movements; for 6 of them were observed during too short a period for any judgment to be formed on this hea<1, |