Cassia sp? (a large S. Brazilian tree raised from seeds sent us [page 117] by F. Müller).—­The cotyledons, after 16 days from their first expansion, had increased greatly in size with two leaves just formed.  They stood horizontally during the day and vertically at night, but were not afterwards observed.

Cassia neglecta (likewise a S. Brazilian species).—­A seedling, 34 days after the first expansion of its cotyledons, was between 3 and 4 inches in height, with 3 well-developed leaves; and the cotyledons, which during the day were nearly horizontal, at night stood vertical, closely embracing the young stem.  The cotyledons of another seedling of the same age, 5 inches in height, with 4 well-developed leaves, behaved at night in exactly the same manner.]

It is known* that there is no difference in structure between the upper and lower halves of the pulvini of leaves, sufficient to account for their upward or downward movements.  In this respect cotyledons offer an unusually good opportunity for comparing the structure of the two halves; for the cotyledons of Oxalis Valdiviana rise vertically at night, whilst those of O. rosea sink vertically; yet when sections of their pulvini were made, no clear difference could be detected between the corresponding halves of this organ in the two species which move so differently.  With O. rosea, however, there were rather more cells in the lower than in the upper half, but this was likewise the case in one specimen of O. Valdiviana. the cotyledons of both species (3 ½ mm. in length) were examined in the morning whilst extended horizontally, and the upper surface of the pulvinus of O. rosea was then wrinkled transversely, showing that it was in a state of compression, and this might have been expected, as the cotyledons sink at night; with O. Valdiviana it was the lower surface which was wrinkled, and its cotyledons rise at night.

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