The Power of Movement in Plants | Page 9

for the first time placed in
this position. The cotyledons bowed themselves greatly towards the
light from 8 to 10.50 A.M., when the first dot was made (Fig. 7).
During the
Fig. 7. Brassica oleracea: conjoint circumnutation of the hypocotyl and
cotyledons, from 10.50 A.M. to 8 A.M. on the following morning.
Tracing made on a vertical glass.
next 12 hours the bead swept obliquely up and down 8 times and
described 4 figures representing ellipses; so that it travelled at nearly
the same rate as in the previous case. during the night it moved
upwards, owing to the sleep-movement of the cotyledons, and
continued to move in the same direction till 9 A.M. on the following
morning; but this latter movement would not have occurred with
seedlings under their natural conditions fully exposed to the light.
By 9.25 A.M. on this second day the same cotyledon had [page 18]
begun to fall, and a dot was made on a fresh glass. The movement was
traced until 5.30 P.M. as shown in (Fig. 8), which is given, because the
course followed was much more irregular than on the two previous
occasions. During these 8 hours the bead changed its course greatly 10
times. The upward movement of the cotyledon during the afternoon
and early part of the night is here plainly shown.

Fig. 8. Brassica oleracea: conjoint circumnutation of the hypocotyl and
cotyledons during 8 hours. Figure here reduced to one-third of the
original scale, as traced on a vertical glass.
As the filaments were fixed in the three last cases to one of the
cotyledons, and as the hypocotyl was left free, the tracings show the
movement of both organs conjoined; and we now wished to ascertain
whether both circumnutated. Filaments were therefore fixed
horizontally to two hypocotyls close beneath the petioles of their
cotyledons. These seedlings had stood for two days in the same
position before a north-east window. In the morning, up to about 11
A.M., they moved in zigzag lines towards the light; and at night they
again became almost upright through apogeotropism. After about 11
A.M. they moved a little back from the light, often crossing and
recrossing their former path in zigzag lines. the sky on this day varied
much in brightness, and these observations merely proved that the
hypocotyls were continually moving in a manner resembling
circumnutation. On a previous day which was uniformly cloudy, a
hypocotyl was firmly secured to a little stick, and a filament was fixed
to the larger of the two cotyledons, and its movement was traced on a
vertical glass. It fell greatly from 8.52 A.M., when the first dot was
made, till 10.55 A.M.; it then rose greatly until 12.17 P.M. Afterwards
it fell a little and made a loop, but by 2.22 P.M. it had risen a little and
continued rising till 9.23 P.M., when it made another loop, and at 10.30
P.M. was again rising. These observations show that the cotyledons
move [page 19] vertically up and down all day long, and as there was
some slight lateral movement, they circumnutated.
Fig. 9. Brassica oleracea: circumnutation of hypocotyl, in darkness,
traced on a horizontal glass, by means of a filament with a bead fixed
across its summit, between 9.15 A.M. and 8.30 A.M. on the following
morning. Figure here reduced to one-half of original scale.
The cabbage was one of the first plants, the seedlings of which were
observed by us, and we did not then know how far the circumnutation
of the different parts was affected by light. Young seedlings were
therefore kept in complete darkness except for a minute or two during

each observation, when they were illuminated by a small wax taper
held almost vertically above them. During the first day the hypocotyl of
one changed its course 13 times (see Fig. 9); and it deserves notice that
the longer axes of the figures described often cross one another at right
or nearly right angles. Another seedling was observed in the same
manner, but it was much older, for it had formed a true leaf a quarter of
an inch in length, and the hypocotyl was 1 3/8 inch in height. The
figure traced was a very complex one, though the movement was not so
great in extent as in the last case.
The hypocotyl of another seedling of the same age was secured to a
little stick, and a filament having been fixed to the midrib of one of the
cotyledons, the movement of the bead was traced during 14 h. 15 m.
(see Fig. 10) in darkness. It should be noted that the chief movement of
the cotyledons, namely, up and down, would be shown on a horizontal
glass-plate only by the lines in the direction of the midrib (that is, [page