The first and succeeding pairs of young true
leaves behaved in exactly the same manner. We think that the movement in
this case may be called nyctitropic, though the angle passed through was
small. The cotyledons are very sensitive to light and will not expand if
exposed to an extremely dim one.
Anoda Wrightii (Malvaceae).--The cotyledons whilst moderately young, and
only from .2 to .3 inch in diameter, sink in the evening from their mid-day
horizontal position to about 35o beneath the horizon. But when the same
seedlings were older and had produced small true leaves, the almost
orbicular cotyledons, now .55 inch in diameter, moved vertically downwards
at night. This fact made us suspect that their sinking might be due merely
to their weight; but they were not in the least flaccid, and when lifted up
sprang back through elasticity into their former dependent position. A pot
with some old seedlings was turned upside down in the afternoon, before the
nocturnal fall had commenced, and at night they assumed in opposition to
their own weight (and to any geotropic action) an upwardly directed
vertical position.
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