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Show 2GG MODIFIED CIROUMNUTATIO~. CIIAl'. v. · 1 st vertical I) lane, mHl therefore descriuo very 111 an a mo . 1 •. 1 . narrow e ll1. 1) S s , \Ylwrcas the mn,ny kmc s <>L ton( n1 s which consist of mctamorpho d leaves, make much broader ellipses or nearly circular fign~cs; and thus they have a far better chance of catchmg ho~d o! a support on any side. rrhe movements of chmbmg pla nt s l1 ave- (a. lso been modified in. some few other RpcC·l a 1 ".a. ys . rrhus the circnmnntatmg stems of Solnanum dulcama?·a can twine ronnel a .support only when this is as thin and flexible as a stnng or thread.. The twining st ms of several. B:·itish plants canno~ t w.i ne round a suppor·t when lt lS more than a fell inches in thickness; whilst in tropiral fore~ts some can emb race thi.c]'~" tr·un1T'-s ·, * ancl thi·s bo-rca.t chfforenc.e in power depends on some unknown dlfference m their manner of circumnutation. The most. remarkable special modification of thi move!ncnt :vlnch w~ have observed is in the tendrils of Echinocyst~s lobata) t.hese are usua1 1 y 1. nc l1' n eel <n• t ac bout 450 above the honzont , but they stiff n and straighten themselves so as ~ stancl uprio·ht in a part of their cir ular course, namel~, when theyb approach aucl ]1 av t o pass 0 ver the sumnutt of the shoot from whw. l ] : If tlwv had no l t 1cy ansc. ' J ll possessed and cxcrCl.s ccl t h'IS cun.o us po"r c. r ' they wou ( infallibly have struck agninst the summit of the shoo~ ancl been arresteLll.n 1 . As soon as one o t wu cour. 0 • · . .ff these tencln. ls w.i th I. ts t h reo b r.a nc·1 1es bcbo· m.s to stl .e n . 11 tl . volvm()' motwn itself and rise up vertwa y, le 10 . 0 d becomes more rap.i d; an d as soon as It has passe < • •1. g . · t ·on cmnc1c lD over the point of chffic~lty, Its mo. l fall into ifs with that from its own weight, causes It to th niJax · · 11 that e " v· I)rcviously inclined positwn so qmc c y, . < t' ·lock. ean be seen trav ell.m g h.k e t h e 11 an<..l of a g·I oa an lC c Cl. b' (Y * • Plants' P· 36. The Movements o.nd Habits of liD 1110 ' CHAP. v. EPINASTY AND HYPONASTY. 267 A large number of ordinary leaves and leaflets ancl a few flower-peduncles are provided with pulvini; but this is not the case with a single tendril at present known. The cause of this difference probably lies in the fact, that the chief service of a pulvinus is to prolong the movement of the part thus provided after growth has ceased; and as tendrils or other climbingorgans are of use only whilst the plant is increasing in height or growing, a pulvinus which served to prolong their movements would be useless. It was shown in the last chapter that the stolons or runners of certain plants circumnutate largely, and that this movement apparently aids them in finding a pas~age between the crowded stems of acljoining plants. If 1t could be proved that their movements had been modified and increased for this special purpose, they ought to have been included in the present chapter; but as the amplitu le of their revolutions is not so con.spicuously different from that of ordinary plants, as m the case of climbers we have no evidence on this head. We encounter ~he same doubt in the case ~f .some p~ants which bury their pods in the ground. ~h1s burymg process is certainly favoured by the cncumnutation of the flower-peduncle; but we do not know whether it has been increased for this special purpose. EPINASTY-HYPONASTY. The term epiuasty is used by De Vries * to express greater longitudinal growth along the upper than in* '.:Arbeiteu des Dot. Inst., D Wur~burg,' Heft ii. 1872, p. 223. (:p~ 2r;Je:h has sl~ghtly modified ) e meaumg of the o.bove two terms as first used by Scbimper, and tl1ey have been adopted in this sense by Sachs. I,. I .• ~ ::: :;~ ..... ,..4' .~t r•;J :J''' .:: |
