The number 89
might have been a little increased, for the cotyledons remained almost
horizontal at night in some species in a few genera, for instance,
Trifolium and Geranium, which are included amongst the sleepers, such
genera might therefore have been added to the 89. Again, one species of
Oxalis generally raised its cotyledons at night more than 20o and less than
60o above the horizon; so that this genus might have been included under
two heads. But as several species in the same genus were not often
observed, such double entries have been avoided.
In a future chapter it will be shown that the leaves of many plants which
do not sleep, rise a few degrees in the evening and during the early part
of the night; and it will be convenient to defer until then the
consideration of the periodicity of the movements of cotyledons.
On the Pulvini or Joints of Cotyledons.--With several of the seedlings
described in this and the last chapter, the summit of the petiole is
developed into a pulvinus,
[page 113]
cushion, or joint (as this organ has been variously called), like that with
which many leaves are provided.
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