Trifolium is a natural genus, and the leaves of all
* Pfeffer, 'Die Period. Bewegungen,' 1875, p. 157.
[page 118]
the species seen by us are pulvinated; so it is with the cotyledons of T.
subterraneum and strictum, which stand vertically at night; whereas those
of T. resupinatum exhibit not a trace of a pulvinus, nor of any nocturnal
movement. This was ascertained by measuring the distance between the tips
of the cotyledons of four seedlings at mid-day and at night. In this
species, however, as in the others, the first-formed leaf, which is simple
or not trifoliate, rises up and sleeps like the terminal leaflet on a
mature plant.
In another natural genus, Oxalis, the cotyledons of O. Valdiviana, rosea,
floribunda, articulata, and sensitiva are pulvinated, and all move at night
into an upward or downward vertical position. In these several species the
pulvinus is seated close to the blade of the cotyledon, as is the usual
rule with most plants. Oxalis corniculata (var. Atro-purpurea) differs in
several respects; the cotyledons rise at night to a very variable amount,
rarely more than 45o; and in one lot of seedlings (purchased under the name
of O.
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