Gossypium herbaceum:  Sensitiveness of the apex of the Radicle.—­Radicles were experimented on in the same manner as before, but they proved ill-fitted for our purpose, as they soon became unhealthy when suspended in damp air.  Of 38 radicles thus suspended, at temperatures varying from 66o to 69o F., with squares of card attached to their tips, 9 were plainly and 7 slightly or even doubtfully deflected from the squares and from the perpendicular; 22 not being affected.  We thought that perhaps the above temperature was not high enough, so 19 radicles with attached squares, likewise suspended in damp air, were subjected to a temperature of from 74o to 79o F., but not one of them was acted on, and they soon became unhealthy.  Lastly, 19 radicles were suspended in water at a temperature from 70o to 75o F., with bits of glass or squares of the card attached to their tips by means of Canada-balsam or asphalte, which adhered rather better than shellac beneath the water.  The radicles did not keep healthy for long.  The result was that 6 were plainly and 2 doubtfully deflected from the attached objects and the perpendicular; 11 not being affected.  The evidence consequently is hardly conclusive, though from the two sets of cases tried under a moderate temperature, it is probable that the radicles are sensitive to contact; and would be more so under favourable conditions.

Fifteen radicles which had germinated in friable peat were suspended vertically over water.  Seven of them served as controls, and they remained quite straight during 24 h.  The tips of the other eight radicles [page 169] were just touched with dry caustic on one side.  After only 5 h. 10 m. five of them were slightly curved from the perpendicular and from the side bearing the little blackish marks.  After 8 h. 40 m., 4 out of these 5 were deflected at angles between 15o and 65o from the perpendicular.  On the other hand, one which had been slightly curved after 5 h. 10 m., now became straight.  After 24 h. the curvature in two cases had considerably increased; also in four other cases, but these latter radicles had now become so contorted, some being turned upwards, that it could no longer be ascertained whether they were still curved from the cauterised side.  The control specimens exhibited no such irregular growth, and the two sets presented a striking contrast.  Out of the 8 radicles which had been touched with caustic, two alone were not affected, and the marks left on their tips by the caustic were extremely minute.  These marks in all cases were oval or elongated; they were measured in three instances, and found to be of nearly the same size, viz. 2/3 of a mm. in length.  Bearing this fact in mind, it should be observed that the length of the curved part of the radicle, which had become deflected from the cauterised side in the course of 8 h. 40 m. was found to be in three cases 6, 7, and 9 mm.