the tip, instead of standing vertically upwards, had become bowed downwards through geotropism, so as almost to touch the zinc plate.  As far as we could roughly ascertain by measurements made with compasses on other seeds, the tip alone, for a length of only 2/100 to 3/100 of an inch, is acted on by geotropism.  But the tracing shows that the basal part of the radicle continued to circumnutate irregularly during the whole time.  The actual extreme amount of movement of the bead at the end of the filament was nearly .05 inch, but to what extent the movement of the radicle was magnified by the filament, which was nearly 3/4 inch in length, it was impossible to estimate.

Fig. 1.  Brassica oleracea:  circumnutation of radicle, traced on horizontal glass, from 9 A.M.  Jan. 31st to 9 P.M.  Feb. 2nd.  Movement of bead at end of filament magnified about 40 times.

Another seed was treated and observed in the same manner, but the radicle in this case protruded .1 inch, and was not Fig. 2.  Brassica oleracea:  circumnutating and geotropic movement of radicle, traced on horizontal glass during 46 hours.

fastened so as to project quite vertically upwards.  The filament was affixed close to its base.  The tracing (Fig. 2, reduced by half) shows the movement from 9 A.M.  Jan. 31st to 7 A.M.  Feb. 2nd; but it continued to move during the whole of the [page 12] 2nd in the same general direction, and in a similar zigzag manner.  From the radicle not being quite perpendicular when the filament was affixed geotropism came into play at once; but the irregular zigzag course shows that there was growth (probably preceded by turgescence), sometimes on one and sometimes on another side.  Occasionally the bead remained stationary for about an hour, and then probably growth occurred on the side opposite to that which caused the geotropic curvature.  In the case previously described the basal part of the very short radicle from being turned vertically upwards, was at first very little affected by geotropism.  Filaments were affixed in two other instances to rather longer radicles protruding obliquely from seeds which had been turned upside down; and in these cases the lines traced on the horizontal glasses were only slightly zigzag, and the movement was always in the same general direction, through the action of geotropism.  All these observations are liable to several causes of error, but we believe, from what will hereafter be shown with respect to the movements of the radicles of other plants, that they may be largely trusted.

Hypocotyl.—­The hypocotyl protrudes through the seed-coats as a rectangular projection, which grows rapidly into an arch like the letter U turned upside down; the cotyledons being still enclosed within the seed.  In whatever position the seed may be embedded in the earth or otherwise fixed, both legs of the arch bend upwards through apogeotropism, and thus rise vertically above the ground.  As soon as this has taken place, or even earlier, the inner or concave surface of the arch grows more quickly than the upper or convex surface; and this tends to separate the two legs and aids in drawing the cotyledons out of the buried seed-coats.  By the growth of the whole arch the cotyledons are ultimately dragged from beneath the ground, even from a considerable depth; and now the hypocotyl quickly straightens itself by the increased growth of the concave side.