of the bean were coated with it for a length of 3 mm., and to our surprise this part increased in length in 23 h. to 7.1 mm.; the thick layer of grease being curiously drawn out.  It thus could not have checked much, if at all, the growth of the terminal part of the radicle.  With respect to geotropism, the tips of seven horizontally extended radicles were coated for a length of 2 mm., and after 24 h. no clear difference could be perceived between their downward curvature and that of an equal number of control specimens.  The tips of 33 other radicles were coated on different occasions for a length of 3 mm.; and they were compared with the controls after 8 h., 24 h., and 48 h.  On one occasion, after 24 h., there was very little difference in curvature between the greased and control specimens; but generally the difference was unmistakable, those with greased tips being considerably less curved downwards.  The whole growing part (the greased tips included) of six of these radicles was measured and was found to have increased in 23 h. from 10 mm. to a mean length of 17.7 mm.; whilst the corresponding part of the controls had increased to 20.8 mm.  It appears therefore, that although the tip itself, when greased, continues to grow, yet the growth of the whole radicle is somewhat checked, and that the geotropic curvature of the upper part, which was free from grease, was in most cases considerably lessened.

Pisum sativum.—­Five radicles, extended horizontally over water, had their tips lightly touched two or three times with dry caustic.  These tips were measured in two cases, and found to be blackened for a length of only half a millimeter.  Five other radicles were left as controls.  The part which is most bowed through geotropism lies at a distance of several millimeters from [page 535] the apex.  After 24 h., and again after 32 h. from the commencement, four of the cauterised radicles were still horizontal, but one was plainly geotropic, being inclined at 45o beneath the horizon.  The five controls were somewhat geotropic after 7 h. 20 m., and after 24 h. were all strongly geotropic; being inclined at the following angles beneath the horizon, viz., 59o, 60o, 65o, 57o, and 43o.  The length of the radicles was not measured in either set, but it was manifest that the cauterised radicles had grown greatly.

The following case proves that the action of the caustic by itself does not prevent the curvature of the radicle.  Ten radicles were extended horizontally on and beneath a layer of damp friable peat-earth; and before being extended their tips were touched with dry caustic on the upper side.  Ten other radicles similarly placed were touched on the lower side; and this would tend to make them bend from the cauterised side; and therefore, as now placed, upwards, or in opposition to geotropism.  Lastly, ten uncauterised radicles were extended horizontally as controls.  After 24 h. all the latter were geotropic; and the ten with