--A young seedling was dimly illuminated
from above, and the circumnutation of the hypo-
[page 22]
cotyl was observed during 28 h., as shown in Fig. 11. It moved in all
directions; the lines from right and to left in the figure being parallel
to the blades of the cotyledons. The actual distance travelled from side to
side by the summit of the hypocotyl was about .2 of an inch; but it was
impossible to be accurate on this head, as the more obliquely the plant was
viewed, after it had moved for some time, the more the distances were
exaggerated.
We endeavoured to observe the circumnutation of the cotyledons, but as they
close together unless kept exposed to a moderately bright light, and as the
hypocotyl is extremely heliotropic, the necessary arrangements were too
troublesome. We shall recur to the nocturnal or sleep-movements of the
cotyledons in a future chapter.
Fig. 12. Gossypium: circumnutation of hypocotyl, traced on a horizontal
glass, from 10.30 A.M. to 9.30 A.M. on following morning, by means of a
filament fixed across its summit. Movement of bead of filament magnified
about twice; seedling illuminated from above.
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