Botany; Geotropism; Plants -- Irritability and movements
Oxalis Valdiviana.—This species is interesting, as the
cotyledons rise perpendicularly upwards at night so as to come into
close contact, instead of sinking vertically downwards, as in the case
of O. rosea. A glass filament was fixed to a cotyledon, .17 of an inch
in length, and the hypocotyl was left free. On the first day the
seedling was placed too far from the vertical glass; so that the
tracing was enormously exaggerated and the movement could not be traced
when the cotyledon either rose or sank much; but it was clearly seen
that the cotyledons rose thrice and fell twice between 8.15 A.M. and
4.15 P.M. Early on the following morning (June 19th) the apex of a
cotyledon was
placed only 1 7/8 inch from the vertical glass. At 6.40 A.M. it stood
horizontally; it then fell till 8.35, and then rose. Altogether in the
course of 12 h. it rose thrice and fell thrice, as may be seen in Fig.
15. The great nocturnal rise of the cotyledons usually commences about
4 or 5 P.M., and on the following morning they are expanded or stand
horizontally at about 6.30 A.M. In the present instance, however, the
great nocturnal rise did not commence till 7 P.M.; but this was due to
the hypocotyl having from some unknown cause temporarily bent to the
left side, as is shown in the tracing. To ascertain positively that the
hypocotyl circumnutated, a mark was placed at 8.15 P.M. behind the two
now closed and vertical cotyledons; and the movement of a glass
filament fixed upright to the top of the hypocotyl was traced until
10.40 P.M. During this time it moved from side to side, as well as
backwards and forwards, plainly showing circumnutation; but the
movement was small in extent. Therefore Fig. 15 represents fairly well
the movements of the cotyledons alone, with the exception of the one
great afternoon curvature to the left.
Fig. 14. Oxalis rosea: conjoint circumnutation of the cotyledons and
hypocotyl, traced from 8.12 A.M. on June 18th to 7.30 A.M. 19th. The
apex of the cotyledon stood only 3 3/4 inches from the vertical glass.
Figure here given one-half of original scale.
Fig. 15. Oxalis Valdiviana: conjoint circumnutation of a cotyledon and
the hypocotyl, traced on vertical glass, during 24 hours. Figure here
given one-half of original scale; seedling illuminated from above.
Oxalis corniculata (var. cuprea).—The cotyledons rise at night to a
variable degree above the horizon, generally about 45°: those on some
seedlings between 2 and 5 days old were found to be in continued
movement all day long; but the movements were more simple than in the
last two species. This may have partly resulted from their not being
sufficiently illuminated whilst being observed, as was shown by their
not beginning to rise until very late in the evening.
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account