growth to the full extent.  The five radicles which were rectangularly bent became fixed in this position, and they continued to grow out horizontally in the peat for a length of about 1 inch during from 4 to 6 days.  By this time new tips had been formed; and it should be remarked that this regeneration occurred slower in the peat than in water, owing perhaps to the radicles being often looked at and thus disturbed.  After the tips had been regenerated, geotropism was able to act on them, so that they now became bowed vertically downwards.  An accurate drawing (Fig. 195) is given on the opposite page of one of these five radicles, reduced to half the natural size.

We next tried whether a shorter exposure to geotropism would suffice to produce an after-effect.  Seven radicles were extended horizontally for an hour, instead of 1 h. 37 m. as in the [page 527] former trial; and after their tips (1.5 mm. in length) had been amputated, they were placed vertically in damp peat.  Of these, three were not in the least affected and continued for days to grow straight downwards.  Four showed after 8 h. 30 m. a mere trace of curvature in the direction in which they had been acted on by geotropism; and in this respect they differed much from those which had been exposed for 1 h. 37 m., for many of the latter were plainly curved in 6 h.  The curvature of one of these four radicles almost disappeared after 24 h.  In the second, the curvature increased during two days and then decreased. the third radicle became permanently bent, so that its terminal part made an angle of about 45o with its original vertical direction.  The fourth radicle became horizontal.  These two, latter radicles continued during two more days to grow in the peat in the same directions, that is, at an angle of 45o beneath the horizon and horizontally.  By the fourth morning new tips had been re-formed, and now geotropism was able to act on them again, and they became bent perpendicularly downwards, exactly as in the case of the five radicles described in the last paragraph and as is shown in (Fig. 195) here given.

Fig. 195.  Vicia faba:  radicle, rectangularly bent at A, after the amputation of the tip, due to the previous influence of geotropism.  L, side of bean which lay on the peat, whilst geotropism acted on the radicle.  A, point of chief curvature of the radicle, whilst standing vertically downwards.  B, point of chief curvature after the regeneration of the tip, when geotropism again acted.  C, regenerated tip.

Lastly, five other radicles were similarly treated, but were exposed to geotropism during only 45 m.  After 8 h. 30 m. only one was doubtfully affected; after 24 h. two were just perceptibly curved towards the side which had been acted on by geotropism; after 48 h. the one first mentioned had a radius of curvature of 60 mm.  That this curvature was due to the action of geotropism during the horizontal position of the radicle, was shown after 4 days, when a new tip had been re-formed, for it then grew perpendicularly downwards.  We learn from this [page 528] case that when the tips are amputated after an exposure to geotropism of only 45 m., though a slight influence is sometimes transmitted to the adjoining part of the radicle, yet this seldom suffices, and then only slowly, to induce even moderately well-pronounced curvature.