These, when the plant is asleep,
are directed forwards and become imbricated. The angle between the two
terminal pinnae was diminished at night, in one case by 15o; and they sank
almost vertically downwards. The hinder pairs of pinnae likewise sink
downwards, but do not converge, that is, move towards the apex of the leaf.
The main petiole does not become depressed, at least during the evening. In
this latter respect, as well as in the sinking of the pinnae, there is a
marked difference between the nyctitropic movements of the present plant
and of Mimosa pudica. It should, however, be added that our specimen was
not in a very vigorous condition. The pinnae of Schrankia aculeata also
sink at night.
Acacia Farnesiana (Tribe 22).--The different appearance presented by a bush
of this plant when asleep and awake is wonderful. The same leaf in the two
states is shown in the following figure (Fig. 160). The leaflets move
towards the apex of the pinna and become imbricated, and the pinnae then
look like bits of dangling string. The following remarks and measurements
[page 382]
do not fully apply to the small leaf here figured.
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