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Show 176 SENSITIVENESS OF TilE APEX 011AI'. III. though slight curvature from tho square ; on the 23rd the tip had curved up above the horizon, and on tho 24th was hooked with tho apex pointing almost to the zenith, as in Fig. 68. No. 6. Square attached on tho 21st; on tho 22nd slightly curved from the square; 23rd more cmvetl ; 25t.h considerably curved; 27th all curvature lost, and the radicle was now directed perpendicularly downwards. No. 7. Square attached on tho 21st; on tho 22nd a trace of curvature from the square, which increased next day, o,nd on tho 24th amounted to a right anglo. It is, therefore, manifest that the apex of the radicle of the oak is highly sensitive to contact, an <l retains its sensitiveness during several clays. The movement thus induced was, however, slower than in any of the previous cases, with the exception of that of Msculus. As with the bean, the terminal growing part, after bending, sometimes straightened itself through the action of geotropism, although the object still remained attached to the tip. The same remarkable experiment was next tried, as in the case of the bean; namely, little squares of exactly the same size of the card-like san<lcu paper and of very thin paper (the thicknesses of which have been given under Vicia faba) w ro attacheu with shellac on opposite sides (as accurately as cou1d. uc done) of the tips of 13 radicles, suspended in damp air, at a temperature of 65°-GGo F. The result was striking, for 9 out of these 13 radicl s became pla.inly, and 1 very slightly, curved from the thid\: paper towards the side bearing the thin paper. In two of these cases the apex became completely hooked after two days; in four cases the deft ction from the per· pendicular and from the side bearing the thick paper, amounted in from two to four dttys to angles of goo, 72°, 60°, and 49°, but in two other cases to only lSo and 15°. It should, however, be stated that in tho CHAP. III. OF THE RADICLE OF ZEA. 177 case in ~vhich the dcfle_ction was 40°, the two square.· had accidentally come mto contact on one side of thP apex, and thus formed a lateral ga.ble; and the deflection was directed in part from this O'able and in part from the thick paper. In three eases balone the radieles were not affer.ted by tho differen ·o in thickness of the· squares of paper attached to their tips, and consequently did not bend away from the siuo bearing tlw stiffer paper. Zea mays : Sensitiveness of the apex of the Radicle to contact.-A large number of trials were made on this plant,. as it was the only monocoty lc<.lon on which we' expenmented. An abstract of the results will suffiec·. In th~ first _Place, 22 germinating seeds were pinnecl to cor~-hds without any object beinO' attached to their r.a~wles, some being exposed to a rempemture of 65°- 66 F., and others to between 74° and 79°; and none of them be?ame curved, though some were a littlE; incline<l to on~ Side. A few were selected, which from having ~ermmated. on sand were crooked, but when su~pemled m dam~ ~11' the terminal part grew straight downwards. This ~act having been ascertained, little squares of the card-hlm pap r \vere affixed with shellac on ~everal o~casions, t? the tips of G8 radicles. Of these he t~rmmal growmg part of 39 became within 2-! h. ~~~S~ICuously curved away from the attached squares h ' kfro~ the perpendicular ; 13 out of the 39 formin o· 00 S WIth th . . d · 0 d eu pomts uected towards the zenith afn th8 fonning 1o ops. M oreover, 7 other radides out' ~ e 68, were slightly and two doubtfully defler.te<l ~m the cards. 'fhere remain 20 which were not ~ ected; but 10 of these ought not to be counted· or one was diseased, two had their tips quite sur~ rounded by shellac, and the sq nares on 7 had slippe(l so as to stand par.a l l e1 to tlI e apex, m. stead of obliquely N |