Now if we were to select by hazard 140 genera,
excluding the Leguminosae, and observed their leaves at night, assuredly
not nearly so many as 19 would be found to include sleeping species. We
here refer exclusively to the plants observed by ourselves.
[page 312]
In our entire list of seedlings, there are 30 genera, belonging to 16
Families, the cotyledons of which in some of the species rise or sink in
the evening or early night, so as to stand at least 60o above or beneath
the horizon. In a large majority of the genera, namely, 24, the movement is
a rising one; so that the same direction prevails in these nyctitropic
movements as in the lesser periodic ones described in the second chapter.
The cotyledons move downwards during the early part of the night in only 6
of the genera; and in one of them, Cannabis, the curving down of the tip is
probably due to epinasty, as Kraus believes to be the case with the leaves.
The downward movement to the amount of 90o is very decided in Oxalis
Valdiviana and sensitiva, and in Geranium rotundifolium. It is a remarkable
fact that with Anoda Wrightii, one species of Gossypium and at least 3
species of Ipomoea, the cotyledons whilst young and light sink at night
very little or not at all; although this movement becomes well pronounced
as soon as they have grown large and heavy.
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