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Show 538 SENSI'l'IVENERS TO GRAVl'l'A'J'ION. 0JIAP. XI. all wore strongly _geotropic, most of them pointing perpendicularly downwards. Ton other mdielc!'l, similarly placed, had their tips touched with caustic on the lower Ride; rtftcr 8 h. t hree were slightly g otropic, but not nearly ~o much o as the least geotropic of tho foregoing !:<Ilocim011s ; fom remrtinou horizontal; and three were cnrvod upwanls iu opposi tion to geotropism. After 1U h. tho tlu o which wore slightly geotropic hac!. become Btrongly so. Of tho fonr J1orizon1al racliclcR, one alone showed a trace of geotropism; of the thr c up-curved rachel s, one retained this curv<thuc, rtnd tho otl1er two hucl beeomc horizonbtl. Tho radiclos of tltiR plant, as rtlrcacly rcnMrke<l, clo not succeed well in damp air, but tbo rcRult of one trial may be briefly given. Nino young mcliclos between ·3 mHl ·G inch in length, with tht-ir tips cauterised and blackened for n. length never exceeding ~ mm., together with eight control specimens, were extended horizontally in cln.mp air. After an intel'val or o11ly 4 h. 10 m. all tho controls were Rlightly geotropic, whilst not one of the cn.uterisod Bpccimem; oxhibitccl :t trace of tlliR action. After 8 h. 35 m , there was the same c1 i l'forcnco between tho two sets, but mthcr more strongly marl.;ccl. J{y this t ime b"ih sets had increased greatly in length. The contl'ols, howcYcr, never became much more nrvocl downwttl'cls; mHl after 21 h. there was no great difference between the two sets in their degree of curvature. Eight young radiclos of nearly equal length (average ·36 inch) were l)lacecl beneath and on peat-earth, ancl wore cxposerl to a temp. of 7G0 -76° F . Thch· t.ips had b on tonchoc l1ransverscly with caustic, and five of them wore blacken ·cl for a length of about 0·5 mm., whilst tllo other t l1rcc were only jnst viHiblycliscolomed. In tho same box thoro were 15 cmli~rol mdicleH, mostly about ·36 inch in length, l>nt Borne raJhor loJJ gOl' and older, and therefore less Rcnsitivc. After 5 h., the 1:) control raclicl s were all more or loss gtotropic : after 9 h., cigM of them wore bent down beneath the horizon at various angles bctwceJt45° and goo, the remaining Rcven boi11g only slightly geotropic : after 2.j h: all were rectangularly geotropic. Tho state of tile eight. cn,ntel'lsccl radicles after the sarno intervals of time was rtR follows: after 5 h. one alone was slightly geotropic, and thjs waR one ':ith the tip only a very little d.iscolomod: aft r 9 h. tl10 one .l118t mentioned was rectangularly gcoh·opic, and two others we~·c slightly so, and these were t he throe which llncl been scarce Y CHAP. XI. TRANSMI'l"l'ED EFVECTS : ZEA. 539 nffeoted by the caustic ; the other ~ive wore still strictly horizontal. After 24 h. 40 m. tho three w1t.h only slightly diRcolourcd tips were bent clown rectangularly ; the other five wore not in tl1e least affected, but several of them had grown rather tornwusly, though still in a horizontn.l plane. The eight cautoriRcd mlicles which bad at first a mean length of ·3G inch, after 9 h. hnd increased to a moan lc11gth of ·79 inch ; and after 24 h. 40 m. to the extraordinary moun 1 ngth of 2 inches. Thoro was no plain dificronce in length between the five well cauterised radicles which remained horizontal, and the three with slightly cauterised tips which had become abruptly bent. clown. A fow of tho control racl.icle!:l wore moaRurocl after 2G h., ancl they were on an average only a little lm1gcr tlut~l the canteri~ccl viz., 2·19 inches. vVc thus soc that killing tho extreme tip of the mdicle of this plant for a length of about 0·5 mm., though it stops the geotropic bending of the uvpcr part, hardly interferes with the growth of tho whole mdiclo. In the same box with tho 15 control specimens, the rapid o·cotropic bending and growth of which luwo jnst been described there were six radicle::;, about ·G inch in length, extended hori~ zontally, from which the tips hncl been cut off in a transverse direction for a length of barely 1 mm. Thcr-;e mdiclcs were examined after 9 h. and agn.in after 24 h. 4.0 m., and they all remained horizontal. They had not become uearly so tortuous as those above described which had been cauterised. Tho radicles with their tips cut ofi' had grown in tho 24 h. 4.0 m. as much, judging by the eye, as tho cauterised Sltocimcns. . Zea muy~.-Tho tip_s of several radiclos, extended horizontally ~n damp a1r, were dnod with l>lotting-papor and then touched m.the first trial during 2 or ;) second· with dry caustic; but tins was too long a contact, for tho tips wore blackened for n length of rathor above 1 mm. They showed no si()'ns of rreo-t . f b b ~p1sw a ter ~_n inttrv~l of .0 h., and '~ere then thrown away. h 11 second tnal tho tips of three rn.chclos were touched for a 8 orter time, and wero blackened for a length of from 0·5 to ~~75 mm.: they all. rem~in cd horizontal for 4 h., hut artcr H h. . m. one of thom, m which the blackcncJ. tip was only 0·5 mm. ml engt.h ' was m· e1 m' e d at 21° beneath tho horizon. Six con- ~o~r:~!Cles nll bcca~e slightly o·ootropic in 4 h ., and ~trougly be 8 h. 30 m., With tho chief scat of curvature generally thtween ~or 7 mm. from the apex. In tho cauterised specimens, e tenrunal growing part, 10 mm. in length, incrcascJ. during |