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Show 166 SENSI'l'IVJ~~E S OF THE APEX C JI Al'. III. of experiments, when the tips of ~cveral were greatly blackened anu injured on one side, so that their growth was arrested, a length of less than 3 mm. became curved towa1·ds the much blackenc<l siue, owing to the continued growth of the opposite side. r:rhi::; difference in the results is interesting, for it shows that too strong an irritant cloes not indu ·c <tny tnm~;mittcd effect, and uoes not cause the adjoining, upper and growing part of the raclicle to b nd. \hl e have analogous cases with Drosera, for a strong solution of carbonate of ammonia when absorbed Ly the ghmcls, or too great heat su<ldenly applied to them, or crushing them, does not cause the basal part of the tentacles to bend, whilst a weak solution of the carbonate, or a moderate heat, or slight pres. nrc always induce.· ::mch bending. Similar results were observed with Dionwa and Pinguicula. The effect of cutting off with a ra~~;or a thin slice from one side of the coni ·al apex of 14 young and short radicles was next tried. Six of them after bein()' operated on were suspended in cb.mp air; th e tips of the other eight, similarly suspen<lcd, \rcre allowed to enter water at a tempentture of about 65° F. It was recorded in each case which side of the apex had been sliced off, and when they were afterwards examineu the direction of tho curvature was noted, before the record was consulted. Of the six ra(lides in damp air, three had their tips curvc<l after an interval of 10 h. 15 m. dir~ctly away from the sliced surface, whilst the other three were not affected and remained straight; nevcrtheles~, one of them after 13 adclitional hours became slightly curve<l from tho sliced surfc.tee. Of the cio·ht rculicl s with their tips b immerse<l in water, seven were phtinly ·urvo<l a":ay from the sliced surfaces after 10 h. 15 m. ; tm<l mth CnAP. Ill. OF 'l'IIE HADICLE 011 'fROPJEOLlJ'l\1. 1G7 respect to the eighth which remained quite straight, too· thick a slice had been aceiclcntally removed, so that it hardly formed a real exception to the general result. vVhen the seven radicl s were looked at again, after an interval of 23 h. from the time of slicing, two had become distorted ; four were cleflectecl at an angle of about 70° from the perpendicular and from the cut surface ; and one was delle ·te<l at nc:trly 90°, so that it projected almost horizontally, lmt with the extreme tip now beginning to bend downwards through the action of geotropism. It is therefore manifest that a thin slice cut off one side of the conical apex, causes the upper growing part of the radicle of this Phaseolu to bend, through the transmitte(l effect. of the irritation, away from the sliced surface. Tropmolum, ma}us : Sensitiveness of the apex of the Radicle to contact.-Little squares of cu.rcl were att.whcd with shellac to one side of the tips of 19 racliclcs, some of which were su1jectecl to 78° F., and others to a much lower temperature. Only 3 became plainly curved from the squares, 5 slightly, 4 doubtfully, and 7 not at all. These seeds were, as we believed, old, so we procured a fresh lot, and now the results were widely different. 'fwcnty-thrcc were tried in the same manner; five of the squares produce<l no ~ffe~t, but three of these cases were no real exceptions, for m two of them the squares had slipped and wer ~arallel to the apex, and in the third the shellac was m excess. and had spread equally all round the apex. One ra~1ele was deflected only slightly from the perpendicular and from the card· whilst seventeen were plainly deflected. The angle; in several of these latter cases varied between 40° and 65° from the perpendicular; and in two of them it amounted after 15 h. or 16 h. to about 90°. In one insta,ncc a loop |