In the next chapter it will be shown
that the nyctitropic movements both of cotyledons and leaves consist of a
modified form of circumnutation.
As in the Leguminosae and Oxalidae, the leaves and the cotyledons of the
same species generally sleep, the idea at first naturally occurred to us,
that the sleep of the cotyledons was merely an early development of a habit
proper to a more advanced stage of life. But no such explanation can be
admitted, although there seems to be some connection, as might have been
expected, between the two sets of cases. For the leaves of many plants
sleep, whilst their cotyledons do not do so--of which fact Desmodium gyrans
offers a good instance, as likewise do three species of Nicotiana observed
by us; also Sida rhombifolia, Abutilon Darwinii, and Chenopodium album. On
the other
[page 315]
hand, the cotyledons of some plants sleep and not the leaves, as with the
species of Beta, Brassica, Geranium, Apium, Solanum, and Mirabilis, named
in our list. Still more striking is the fact that, in the same genus, the
leaves of several or of all the species may sleep, but the cotyledons of
only some of them, as occurs with Trifolium, Lotus, Gossypium, and
partially with Oxalis.
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