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Show 174 SENSI'l'IVl~NERR OP 'l'lm .APEX CIIAP. ur. slightly tnwctrds the cauterised sido on tho first da.y, and continuin()' to do so for the noxt three dayR, when tl1e defl ection n.mou~ed to about 90° from the porpcndicnlar. 'l'lte cauRe appeared to lie in the tendril-like Rem;itivcnc ·s of the upper part of the radicle, against which the point of a largo triangular ftap of the seed-coats pressed with consid.crablc force ; aml this irritation apparently conquered that from the cauteriRed fLpcx. rrhose several cases show bcyoll<l doubt that tbP irritation of one side of tho apex, excite· the uppcl' part of the radicle to bend slowly town.r1ls the oppo. ito 'i<le. rrhis faet was well exhibit <1 in 011C lot of five seeds pinned to the cork-licl of a jar; for \rh en after () days the lid was turn cl npsi<lo <lown an<l Yicwed from cliroctl y alwvo, the 1i ttl black marks nHLde by the eanstic were now all distinctly visible on the upper sides of the tips of tho lateraJly bowc<lrrt<liel es. A thin slice was shavo<l off with a rn~:or from Olll' .·ide of tho tips of 22 ra(lidcs, in th<' mn.nn ur 1lcscriucd mulor tho common ben.n; bnt this kjnd of irritation did not provo very effooti vc. Only 7 out of the 2~ ntclicles became mO<leratcly defleetccl in from 3 to 5 days from tho 1icoc1 snrfn.c·r, ancl s voral of the othrt" grew irregularly. 1'ho ovidonco, therefore, i. f,u· from l'Onclusivo. (Jum·cus robur: Sensitiveness of the apex of the Radicle. - The tips of the radicles of tho common Ottk arc i1dly as sensitive to slight conta ·t as arc tho.·e of <UJY pliiJ~t examined by ns. They remain c1 healthy in damp all' for 10 days, but grow slowly. R<tnarcs of the eanllike paper wore fixed with sh lhw to the tips of 15 racliclos, and ton of these boeamo cmtspicuonsly Loll'ed from the perpendicular and from the squares ; two slightly, and three not at all. But two of the htttcr were not real exceptions, as they were at first very short., and hardly grew afterwards. Some of the more CHAP. III. OF 'l'HE UA lHCLJ£ OF QUEHUUR. 17.3 remarkable cases arc worth closcribing. rrho radiclcs were examined on onch successive morning, at nearly the same hour, that is, after intervals of 24 h. No. 1. This radicle suffered from a Rorh:R of acciilents, and acted in an anomalous manner, for tllC apex a.ppcaTed at firRt insensible and afterwards sensitive to contact. Tho fm.;t square was attached on Oct. 19th ; on the 21st the · mdicle was not at all curved, and the square Fig. 68. was accidentally knocked off; it was rcfixc l on the 22ncl, and the radicle became Blightly curved from the Bqua.ro, but the cnrvaturc disappeared on the 23rd, when the sqnare was removed and refixed. No curvature ensued, and the square was again accidentally knocked off, and refixed. Ou tho morning of the 27th it was washed off hy having reach eel the water in the bottom of the iar. Tho square was refL'wd, ancl on the 29th, that is, ten clays after the first square had been attached, and two dayK after tho attnchment of the last square, the rndiclo had grown to the great length of 3·2 inches, and now Quc1·cus nJmr: radi cle the terminal growing ]Jart had become bent with st1uare of card away from the square into a hook (soc attaehcJ to one side Fig. 68). of apex. causing it to be •ome hooked. No. 2. Square attached on the 19th; on Drawing one-half' the 20th radicle slightly deflected from it natural scale. and from the perpendicular; on tbe 21st d.cftected at nearly right angles ; it remained duriug the next two days in this position, but on the 25th tho upward curvature was lessened through the n.ction of geotropism, and .'till more so on the 26th. No. 3. Square attached on the 1Dt.h; on tltc 21st a trace of curvature from the Sf!uaro, which amounted on the 22nd to about 40°, and on tho 23rcl to 53° from the perpendicular. No. 4. Square attached on tho 21st; on the 22nd trace of c~rvature f~·om the square ; on tho 23rd completely hooked ~lth the pomt turned up to the zenith. Throe days afterwards (I.~. 26th) the curvature had wholly disappeared and the apex pomted perpendicularly downwards. No. 5. Square attached on the 21st; on the 22nd deciclecl |