Again, when both the cotyledons and the leaves of
the same plant sleep, their movements may be of a widely dissimilar nature:
thus with Cassia the cotyledons rise vertically up at night, whilst their
leaves sink down and twist round so as to turn their lower surfaces
outwards. With seedlings of Oxalis Valdiviana, having 2 or 3 well-developed
leaves, it was a curious spectacle to behold at night each leaflet folded
inwards and hanging perpendicularly downwards, whilst at the same time and
on the same plant the cotyledons stood vertically upwards.
These several facts, showing the independence of the nocturnal movements of
the leaves and cotyledons on the same plant, and on plants belonging to the
same genus, lead to the belief that the cotyledons have acquired their
power of movement for some special purpose. Other facts lead to the same
conclusion, such as the presence of pulvini, by the aid of which the
nocturnal movement is continued during some weeks. In Oxalis the cotyledons
of some species move vertically upwards, and of others vertically downwards
at night; but this great difference within the same natural genus is not so
surprising as it may at first appear, seeing that the cotyledons of all the
species are continually oscillating up and down during the day, so that a
small cause might determine whether they should rise or sink at night.
Pages:
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532