A filament was fixed across the pod with a mark
beneath, and its move-
[page 435]
ment, greatly magnified, was traced on a horizontal glass during 67 h. The
plant was illuminated during the day from above. A copy of the tracing is
given on p. 434 (Fig. 179); and there can be no doubt that the descending
movement is one of modified circumnutation, but on an extremely small
scale. The observation was repeated on another pod, which had partially
buried itself in sawdust, and which was lifted up a quarter of an inch
above the surface; it described three very small circles in 24 h.
Considering the great length and thinness of the peduncles and the
lightness of the pods, we may conclude that they would not be able to
excavate saucer-like depressions in sand or sawdust, or bury themselves in
moss, etc., unless they were aided by their continued rocking or
circumnutating movement.]
Relation between Circumnutation and Heliotropism.--Any one who will look at
the foregoing diagrams, showing the movements of the stems of various
plants towards a lateral and more or less dimmed light, will be forced to
admit that ordinary circumnutation and heliotropism graduate into one
another.
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