OCR Text |
Show 30-± MODIFIED CIRCU:\1NUTATION. Crr.11>. VI. Cucut·bitacccc.-The cotyledons of C'ucn1·bita anmntin and ov£fera and of Lagenur'ict vulgar· is, stand from the 1st to tho 3rd day of ti1eir life at about 60° above the horizon, and at night rise UIJ so as to become vertical and in close contact with one another. With Ottcttmis dudaim they stood at noon at 45° above the horizon and closed at night. The tips of the cotyledons of all these spe~ics n.re, however, 1·eftexed, s~ t!1n.t ~his part is fully expo ~d to the zenith at night; n.nd tJus fact IS opposed to tho behcf that the movement is of the sallle nature as that of sleeping phmts. After the first two or three clays the cotyle~lons divcrcre more during the du.y and cease to close at mght. Thos; of 'J'richosanthes anguina arc somewhat thick and fleshy, and did not rise at night; and they could p rhap. hardly be expected to do so. On the other hn.ncl, those of .Ll ca,thosicy~s hor·rid~6 * present nothing in their n.ppcn.rn.nce op]lo_secl to t~mr moving at night in the smnc mn.nncr as the preced:n~ specres; yet they clid not rise up in n.ny pbin manner. Thrs fact leads to the belief that the noctumal movements of the above-named species has been acquired for some specin.l pmposo, which may be to protect tho young plumule from raditttion, by the close contact of the whole basal portion of the two cotyledons. (f, muiUin mtuudVolilon (Gcmniacc:1·).-A r-;inglc seccllingcamo up accidentally in a. pot, n.nrl its cotyl?clous were ohservecl.to bend perpendicularly down wanls clurmg several . succcssrve nio·hts having been horizontal at no u. It grew mto a fine pl~nt but died before flowering : it was s~nt to Kow ~t:cl pronouncccl to be certainly a Geranium, and m all probalnlrty the above-named species. This case i: remarkable bocaus~ the Cotyledons of G. ci11ere~tm End1·essi1;, lbericum, Richantsom: ancl subcuu.ltsccns were observ'e d <luring some weeks. m· tl lewm ter 0 ' and they did not sink, whilst those of G. J btncum roRe 27 at night. . . A u· "had its coty- .Apium petrosel-tnum (Umbelhfcrro).- seer ~no . b ledons (Nov. 22nd) almost fully cxpn.ndc<l dunng tlrc day, Y 8 30 P.M they had r'l·s en consi·d crn.b.ly, an d a t 10 ·3 0 P· M t. were . . . l Jar 0n almost closed their tips being only 1 ~o of an me 1 ~l h · t the followm. g m' ornm. g (23r d) t1lc t·1 ps wer.e 15o so of an me apar' * This plant, from Dammara Land in S. Africa, is remarkable from being tbe one known member of the Family which is not a climber ; . 1 b described 1 t Jas. ecn , xx\'ii. in • 'l'ransact. Lmn. Soc., p. 30. CHAP. VI. SLEEP OF COTYLEDONS. 305 or more than seven times as much. On tho next night the cotyledons occupied nearly the same position as before. On the morning of the 24th they stood horizontally, and at night were 60° above the horizon; and so it was on the night of the 25th. But four days afterwards (on the ~9th), when the seeulings were a week old, the cotyledons had ceased to ri e at niO'ht to any plain degree. 0 Apium graveolens.-Tho cotyledons at noon were horizontal, and at 10 P.M. stood at an angle of 61° above the horizon. Lactuca scariula (Compositre).-The cotyledons whilst young stood sub-horizontally during the day, and at night ro e so a~ to be almost vertical, and some were quite vertical and closed; but this movement ceased when they had grown old and large after an interval of 11 days. ' Helianthtts annuus (Compositm).-This case is rather doubtful· the cotyledons rise at night, and on one occasion they stood at 73o above the horizon, so that they might then be said to have been asleep. lpomcea crerulea vel Plwrbitis nil (Convolvulacem).-The cotyledons be~ave in nearly the same manner as those of the Anoda. and Nankm cotton, and like them grow to a large size. Whilst !oun~ and small, so that their blades were from ·5 to ·6 of an mch m length, measured along the middle to the base of the central notch, they remained horizontal both during the middle : t~e day and at night. As they increa ed in size they began smk more and more in the evening and early night · and when they had grown to a length (mea ·m·ed in the ~bove manner) of from J to 1·25 inch, they sank between 55° and 70,., ~neath the horizon. They acted, however, in this manner only ~~ ~n they had been well illuminated dm·ing the day. Nevert e ess, the cotyledons have little or no power of bendino· tow~rds a lateral light, although the hypocotyl is strongly helio~ toropiC. They are not provided with a pulvinu but continue grow for a long time ' 1 . b hpom~a :purpureu (vel Phar·bitis hispido.).-The cotyledom COet alvde In all respects like those of I. crerulea. A seedlinO' witl~ Y e ons ·75 · h · b . h. me m length (measured as before) and 1·65 ~~c5.3~ Pbreadth, hav~ng a s~all true leaf developed, was placed wei ht n.M. on a ~hnostat m a darkened box, so that neither ledg tooor geotropism could act on them. At 10 p M one coty-on s d at 77o d tl h . . Before . an le ot er at S2o beneath the horizon. bemg placed in the klinostu.t they stood at 15° and 2!:.1° X . ,. ,;.I ,.., ,,,, |