Some trials were next made by irritating the tips without any object being left in contact with them.  Nine radicles, suspended over water, had their tips rubbed, each six times with a needle, with sufficient force to shake the whole bean; the temperature was favourable, viz. about 63o F. In 7 out of these cases no effect whatever was produced; in the eighth case the radicle became slightly deflected from, and in the ninth case slightly deflected towards, the rubbed side; but these two latter opposed curvatures were probably accidental, as radicles do not always grow perfectly straight downwards.  The tips of two other radicles were rubbed in the same manner for 15 seconds with a little round twig, two others for 30 seconds, and two others for 1 minute, but without any effect being produced.  We may therefore conclude from these 15 trials that the radicles are not sensitive to temporary contact, but are acted on only by prolonged, though very slight, pressure.

We then tried the effects of cutting off a very thin slice parallel to one of the sloping sides of the apex, as we thought that the wound would cause prolonged irritation, which might induce bending towards the opposite side, as in the case of an attached object.  Two preliminary trials were made:  firstly, slices were cut from the radicles of 6 beans suspended in damp air, with a pair of scissors, which, though sharp, probably caused considerable crushing, and no curva-[page 150] ture followed.  Secondly, thin slices were cut with a razor obliquely off the tips of three radicles similarly suspended; and after 44 h. two were found plainly bent from the sliced surface; and the third, the whole apex of which had been cut off obliquely by accident, was curled upwards over the bean, but it was not clearly ascertained whether the curvature had been at first directed from the cut surface.  These results led us to pursue the experiment, and 18 radicles, which had grown vertically downwards in damp air, had one side of their conical tips sliced off with a razor.  The tips were allowed just to enter the water in the jars, and they were exposed to a temperature 14o — 16o C. (57o — 61o F.).  The observations were made at different times.  Three were examined 12 h. after being sliced, and were all slightly curved from the cut surface; and the curvature increased considerably after an additional 12 h.  Eight were examined after 19 h.; four after 22 h. 30 m.; and three after 25 h.  The final result was that out of the 18 radicles thus tried, 13 were plainly bent from the cut surface after the above intervals of time; and one other became so after an additional interval of 13 h. 30 m.  So that only 4 out of the 18 radicles were not acted on.  To these 18 cases the 3 previously mentioned ones should be added.  It may, therefore, be concluded that a thin slice removed by a razor from one side of the conical apex of the radicle causes irritation, like that from an attached object, and induces curvature from the injured surface.