Many trials were made, by coating the tips of horizontally extended radicles with the before described thick grease.  The geotropic curvature of 12 radicles, which were thus coated for a length of 2 mm., was delayed during the first 8 or 9 h., but after 24 h. was nearly as great as that of the control specimens.  The tips of nine radicles were coated for a length of 3 mm., and after 7 h. 10 m. these stood at an average angle of 30o beneath the horizon, whilst the controls stood at an average of 54o.  After 24 h. the two lots differed but little in their degree of curvature.  In some other trials, however, there was a fairly well-marked difference after 24 h. between those with greased tips and the controls.  The terminal part of eight control specimens increased in 24 h. from 10 mm. to a mean length of [page 537] 24.3 mm., whilst the mean increase of those with greased tips was 20.7 mm.  The grease, therefore, slightly checked the growth of the terminal part, but this part was not much injured; for several radicles which had been greased for a length of 2 mm. continued to grow during seven days, and were then only a little shorter than the controls.  The appearance presented by these radicles after the seven days was very curious, for the black grease had been drawn out into the finest longitudinal striae, with dots and reticulations, which covered their surfaces for a length of from 26 to 44 mm., or of 1 to 1.7 inch.  We may therefore conclude that grease on the tips of the radicles of this Phaseolus somewhat delays and lessens the geotropic curvature of the part which ought to bend most.

Gossypium herbaceum.—­The radicles of this plant bend, through the action of geotropism, for a length of about 6 mm.  Five radicles, placed horizontally in damp air, had their tips touched with caustic, and the discoloration extended for a length of from 2/3 to 1 mm.  They showed, after 7 h. 45 m. and again after 23 h., not a trace of geotropism; yet the terminal portion, 9 mm. in length, had increased on an average to 15.9 mm.  Six control radicles, after 7 h. 45 m., were all plainly geotropic, two of them being vertically dependent, and after 23 h. all were vertical, or nearly so.

Cucurbita ovifera.—­A large number of trials proved almost useless, from the three following causes:  Firstly, the tips of radicles which have grown somewhat old are only feebly geotropic if kept in damp air; nor did we succeed well in our experiments, until the germinating seeds were placed in peat and kept at a rather high temperature.  Secondly, the hypocotyls of the seeds which were pinned to the lids of the jars gradually became arched; and, as the cotyledons were fixed, the movement of the hypocotyl affected the position of the radicle, and caused confusion.  Thirdly, the point of the radicle is so fine that it is difficult not to cauterise it either too much or too little.  But we managed generally to overcome this latter difficulty, as the following experiments