Cucurbita ovifera:  Sensitiveness of the apex of the Radicle.—­The tips proved ill-fitted for the attachment of cards, as they are extremely fine and flexible.  Moreover, owing to the hypocotyls being soon developed and becoming arched, the whole radicle is quickly displaced and confusion is thus caused.  A large number of trials were made, but without any definite result, excepting on two occasions, when out of 23 radicles 10 were deflected from the attached squares [page 170] of card, and 13 were not acted on.  Rather large squares, though difficult to affix, seemed more efficient than very small ones.

We were much more successful with caustic; but in our first trial, 15 radicles were too much cauterised, and only two became curved from the blackened side; the others being either killed on one side, or blackened equally all round.  In our next trial the dried tips of 11 radicles were touched momentarily with dry caustic, and after a few minutes were immersed in water.  The elongated marks thus caused were never black, only brown, and about ½ mm. in length, or even less.  In 4 h. 30 m. after the cauterisation, 6 of them were plainly curved from the side with the brown mark, 4 slightly, and 1 not at all.  The latter proved unhealthy, and never grew; and the marks on 2 of the 4 slightly curved radicles were excessively minute, one being distinguishable only with the aid of a lens.  Of 10 control specimens tried in the same jars at the same time, not one was in the least curved.  In 8 h. 40 m. after the cauterisation, 5 of the radicles out of the 10 (the one unhealthy one being omitted) were deflected at about 90o, and 3 at about 45o from the perpendicular and from the side bearing the brown mark.  After 24 h. all 10 radicles had increased immensely in length; in 5 of them the curvature was nearly the same, in 2 it had increased, and in 3 it had decreased.  The contrast presented by the 10 controls, after both the 8 h. 40 m. and the 24 h. intervals, was very great; for they had continued to grow vertically downwards, excepting two which, from some unknown cause, had become somewhat tortuous.

In the chapter on Geotropism we shall see that 10 radicles of this plant were extended horizontally on and beneath damp friable peat, under which conditions [page 171] they grow better and more naturally than in damp air; and their tips were slightly cauterised on the lower side, brown marks about ½ mm. in length being thus caused.  Uncauterised specimens similarly placed became much bent downwards through geotropism in the course of 5 or 6 hours.  After 8 h. only 3 of the cauterised ones were bowed downwards, and this in a slight degree; 4 remained horizontal; and 3 were curved upwards in opposition to geotropism and from the side bearing the brown mark.  Ten other specimens had their tips cauterised at the same time and in the same degree, on the upper side; and this, if it produced any effect, would tend to increase the power of geotropism; and all these radicles were