Rate of Movement.--The movements of the hypocotyls and cotyledons of
seedling cabbages of different ages have now been sufficiently illustrated.
With respect to the rate, seedlings were placed under the microscope with
the stage removed, and with a micrometer eye-piece so adjusted that each
division equalled 1/500 inch; the plants were illuminated by light passing
through a solution of bichromate of potassium so as to eliminate
heliotropism. Under these circumstances it was interesting to observe how
rapidly the circumnutating apex of a cotyledon passed across the divisions
of the micrometer. Whilst travelling in any direction the apex generally
oscillated backwards and forwards to the extent of 1/500 and sometimes of
nearly 1/250 of an inch. These oscillations were quite different from the
trembling caused by any disturbance in the same room or by the shutting of
a distant door. The first seedling observed was nearly two inches in height
and had been etiolated by having been grown in darkness. The tip of the
cotyledon passed across 10 divisions of the micrometer, that is, 1/50 of an
inch, in 6 m. 40 s. Short glass filaments were then fixed vertically to the
hypocotyls of several seedlings so as to project a little above the
cotyledons, thus exaggerating the rate of movement; but only a few of the
observations thus made are worth giving. The most remarkable fact was the
oscillatory movement above described, and the difference of rate at which
the point crossed the divisions of the micrometer, after short intervals of
time. For instance, a tall not-etiolated seedling had been kept for 14 h.
in darkness; it was exposed before a north-east window for only
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two or three minutes whilst a glass filament was fixed vertically to the
hypocotyl; it was then again placed in darkness for half an hour and
afterwards observed by light passing through bichromate of potassium. The
point, oscillating as usual, crossed five divisions of the micrometer (i.e.
1/100 inch) in 1 m. 30 s. The seedling was then left in darkness for an