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Show IG2 SENSl'I'IVENESS OF 'l'liE Al'EX. CHAP. HI. ueen longer obsorve<l, tho tip no dou~t would have b ~Ollll'l ao·ain curved clom1, all<l It would have een 11 ' o . '1 h lf l formed a loop as in the followmg case. c twc t 1 radicle after 6 h. was slightly curved .uownwarcls; but when looked at again after 21 h., tlns curvature haa disappeared and tho apex pointed u1nYarcls\; a(;'~~'r 3G~ h). the radicle forme<l a hook, as shown ~tt A .t! 1g. 1 ; which hook after 45 h. w<:ts converted. Into a loop (B). 'fhe thirteenth radicle <tf'tcr 6 h. was slightly curved downwards but within 21 h. hacl cnrvecl consi<lcrably up, an d the'n clown aooc·a in at an. an·g le of 4.5 ° 1eneath the horizon, afterwards becoming perpencl1 c~la:·· .In these three la t cases geotropism ancl tho unta~10n causecl uy the c.tttached squares alternately. prcvm.lcd in a highly remarkable manner; gootropt::;m bomg ultimately victorious. . Similar experiments were not <tl ways .qutte so. sue· cessful as in the above cases. 'fhus 6 rad10les, h?nzon· tally extendocl with attached sqnarrs, ':ere tn ed on June 8th at a proper temperatur , and after 7 h. 30m. none were in the least curved upwar<ls and none were distinctly geotropic; ·whereas of 6 radidcs witho~tt rtny attached squares, which sorve<l as standards of com· pan.s on or cont ro l s, 3 b ecn,m o sll. oo ·htly an c.l 3 almost rectangularly geotropic within the 7 h. 30 1~.; but after 23 h. tho two lots were equally gootropw. On July lOth another trial was made with G ?orizontally extended raclicles, with squares attached m the same manner beneath their tips; aml after 7 h. 30m., 4 were slightly geotrovie, 1 rema1· ned hon·z ont a}, am} 1 .W ''\ S curved upwaru_, s m· opposi·t ·w n t o gnwI 'ty or geotr.o p1sn1a.t This latter radicle after 48 h. formed a loop, hke tb at B (Fig. 67). . t d of An analogous trial was now macle, but ms ea h attaching squares of card to the lo·wer sides of t e CnAP. III. OF 'l'JlE JtADICLE OJ~' PHASEOT,U, '. J G:-1 tips, these were tonchnd with clry cl'mstic. The <lctails of the experiment wilJ be given in the ehaptcr 011 Geotropism, and it will snffke here to say that 10 peas, with radicles extend '<l horizontally nncl not cauterised, were laid on and nn(ler damp fri <:-tl )le peat : these, which servou as sttmllanl or controls, as wc•Jl n:-:; 10 others which harl been touched on the nppe1· side with the caustic, all became strongly ~cotropi e in 24 l1. Nine racliclcs, similarly placecl, had th i r tip touchecl on the lower sicle "·ith the caustic; and after 24 h., 3 were slightly O'eotropic, 2 remainc<l horizontal, ancl ±were bowed upwarcls in opposition to o·ravity and to geotropism. ~J..1his upward <"Urvatnre wa clistinetly Yisible in 8 h. 45 m. after tho lower . icl0s of the ti 1;~ · had been cauterised. Little squares of car<l were affixe(l 'rith shellac on two occasions to the tips of 2::>. young and short secondary radicles, which had he n mitt <l from tlw primary n-vliclo whilst oTowing in water, lmt were no" suspended in damp air. ]J<'::;id 'S the cliffienltv of attaching the squares to . uc.:h finely l)Oint cl ol)} eot~ as wer~ these raclic-1 s, the tempcmhtrP Wtts too hjgh. -varymg on the :first oceasion from 72° to 77° P., an< l on the second being almo -t ste<ulily 78° P.; and thi probably lessened the sen. itjvm1rss of th tip. . Tlt~· ~~gnlt ~as that after an interval of 8 lt. 30 m., () of tlH in rachc~e~ were l>ow~d upw<:trds (on of thPm oTeatly) . oppositlOn to gravity, and 2 latcralJv · tho remaiJt-mgl4 were not affected. CunSH· l T·m g·' t' ho nnfavom-able circumstances, and bem·ino· in mind the case < ' !~e b~an, the evidence appears ufficiont to show th:tc e .t~ps of tho secondary mclicles of the pea art· sensitive to slight contact. R ~l~aseolus m1tltijlorus: SensiNveness of the apex of th~· a ~cle.-Fifty-nine raclicles were tried with sqmtre-::. M 2 |
