As it was,
the cotyledon moved up and down in the course of 16 h. 20 m. (i.e. between
6.10 A.M. and 10.30 P.M.) thirteen times.
Fig 35. Ipomoea caerulea: circumnutation of cotyledon, traced on vertical
glass, from 6.10 A.M. June 21st to 6.45 A.M. 22nd. Cotyledon with petiole
1.6 inch in length, apex of blade 4.1 inch from the vertical glass; so
movement not greatly magnified; temp. 20o C.
The cotyledons of this seedling sank downwards during both evenings and the
early part of the night, but rose during the latter part. As this is an
unusual movement, the cotyledons of twelve other seedlings were observed;
they stood almost or quite horizontally at mid-day, and at 10 P.M. were all
declined at various angles. The most usual angle was between 30o and 35o;
but three stood at about 50o and one at even 70o beneath the horizon. The
blades of all these cotyledons had attained almost their full size, viz.
from 1 to 1 ? inches in length, measured along their midribs. It is a
remarkable fact that whilst young--that is, when less than half an inch in
length, measured in the same manner--they do not sink
[page 49]
downwards in the evening.
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