We have now seen that the leaflets in the six genera of Phaseoleae observed by us (with the exception of the primary leaves of Phaseolus Roxburghii) all sleep in the same manner, namely, by sinking vertically down.  The movements of the petioles were observed in only three of these genera.  They rose in Centrosema and Phaseolus, and sunk in Amphicarpaea.

Sophora chrysophylla (Tribe 10).—­The leaflets rise at night, and are at the same time directed towards the apex of the leaf, as in Mimosa pudica.

Caesalpinia, Hoematoxylon, Gleditschia, Poinciana.—­The leaflets of two species of Caesalpinia (Tribe 13) rose at night.  With Haematoxylon Campechianum (Tribe 13) the leaflets move forwards at night, so that their midribs stand parallel to the petiole, and their now vertical lower surfaces are turned outwards (Fig. 153).  The petiole sinks a little.  In Gleditschia, if we understand correctly Duchartre’s description, and in Poin-[page 369] ciana Gilliesii (both belonging to Tribe 13), the leaves behave in the same manner.

Fig. 153.  Haematoxylon Campechianum:  A, branch during daytime; B, branch with leaves asleep, reduced to two-thirds of natural scale.

Cassia (Tribe 14).—­The nyctitropic movements of the leaves in many species in this genus are closely alike, and are highly complex.  They were first briefly described by Linnaeus, and since by Duchartre.  Our observations were made chiefly on C. floribunda* and corymbosa, but several other species were casually observed.  The horizontally extended leaflets sink down vertically at night; but not simply, as in so many other genera, for each leaflet rotates on its own axis, so that its lower surface faces outwards.  The upper surfaces of the opposite leaflets are thus brought into contact with one another beneath the petiole, and are well protected (Fig. 154).  The rotation and other movements are effected by means of a well-developed pulvinus at the base of each leaflet, as could be plainly seen when a straight narrow black line had been painted along it during the day.  The two terminal leaflets in the daytime include rather less than a right angle; but their divergence increases greatly whilst they

* I am informed by Mr. Dyer that Mr. Bentham believes that C. floribunda (a common greenhouse bush) is a hybrid raised in France, and that it comes very near to C. laevigata.  It is no doubt the same as the form described by Lindley (’Bot.  Reg.,’ Tab. 1422) as C. Herbertiana. [page 370]

sink downwards and rotate, so that they stand laterally at night, as may be seen in the figure.  Moreover, they move somewhat backwards, so as to point towards the base of the petiole.

Fig. 154.  Cassia corymbosa:  A, plant during day; B, same plant at night.  Both figures copied from photographs.