The sky varied in brightness, and the seedlings occasionally
Fig. 175. Tropaeolum majus: heliotropic movement and circumnutation of the
epicotyl of a young seedling towards a dull lateral light, traced on a
horizontal glass from 7.48 A.M. to 10.40 P.M. Figure reduced to one-half of
the original scale.
received for a short time less light from the window than from the opposite
side (as ascertained by the shadow cast), and then one of the blinds was
temporarily removed. In the evening the blinds were taken away, one by one.
the course pursued by an epicotyl under these circumstances is shown in
Fig. 175. During the whole day, until 6.45 P.M., it plainly bowed itself
towards the light; and the tip moved over a considerable space. After 6.45
P.M. it moved backwards, or from the window, till
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10.40 P.M., when the last dot was made. Here, then, we have a distinct
heliotropic movement, effected by means of six elongated figures (which if
dots had been made every few minutes would have been more or less elliptic)
directed towards the light, with the apex of each successive ellipse nearer
to the window than the previous one.
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