30 P.M. on
this same day, the crown of the former arch or hook had become perfectly
straight and vertical. There can therefore be no doubt that the
straightening of the hooked shoot of this plant is effected by the
circumnutation of the arched portion--that is, by growth alternating
between the upper and lower surface, but preponderant on the lower surface,
with some little lateral movement.
We were enabled to trace the movement of another straightening shoot for a
longer period (owing to its slower growth and to its having been placed
further from the vertical glass), namely, from the early morning on July
13th to late in the evening of the 16th. During the whole daytime of the
14th, the hook straightened itself very little, but zigzagged and plainly
circumnutated about nearly the same spot. By the 16th it had become nearly
straight, and the tracing was no longer accurate, yet it was manifest that
there was still a considerable amount of movement both up and down and
laterally; for the crown whilst continuing to straighten itself
occasionally became for a short time more curved, causing the filament to
descend twice during the day.
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