Had the above plant been subjected to a higher temperature than 67o — 70o F., the movements of the terminal leaflet would probably have been even more rapid and wider in extent than those shown in the diagram; for a plant was kept for some time in the hot-house at from 92o — 93o F., and in the course of 35 m. the apex of a leaflet twice descended and once ascended, travelling over a space of 1.2 inch in a vertical direction and of .82 inch in a horizontal direction.  Whilst thus moving the leaflet also rotated on its own axis (and this was a point to which no attention had been before paid), for the plane of the blade differed by 41o after an interval of only a few minutes.  Occasionally the leaflet stood still for a short time.  There was no jerking movement, which is so characteristic of the little lateral leaflets.  A sudden and considerable fall of temperature causes the terminal leaflet to sink downwards; thus a cut-off leaf was immersed in water at 95o F., which was slowly raised to 103o F., and afterwards allowed to sink to 70o F., and the sub-petiole of the terminal leaflet then curved downwards.  The water was afterwards [page 360]

Fig. 150.  Desmodium gyrans:  circumnutation and nyctitropic movement of leaf (3 3/4 inches in length, petiole included) during 48 h.  Filament affixed to midrib of terminal leaflet; its apex 6 inches from the vertical glass.  Diagram reduced to one-third of original scale.  Plant illuminated from above.  Temp. 19o — 20o C. [page 361]

raised to 120o F., and the sub-petiole straightened itself.  Similar experiments with leaves in water were twice repeated, with nearly the same result.  It should be added, that water raised to even 122o F. does not soon kill a leaf.  A plant was placed in darkness at 8.37 A.M., and at 2 P.M. (i.e. after 5 h. 23 m.), though the leaflets had sunk considerably, they had by no means acquired their nocturnal vertically dependent position.  Pfeffer, on the other hand, says* that this occurred with him in from 3/4 h. to 2 h.; perhaps the difference in our results may be due to the plant on which we experimented being a very young and vigorous seedling.

The Movements of the little Lateral Leaflets .—­These have been so often described, that we will endeavour to be as brief as possible in giving a few new facts and conclusions.  The leaflets sometimes quickly change their position by as much as nearly 180o; and their sub-petioles can then be seen to become greatly curved.  They rotate on their own axes, so that their upper surfaces are directed to all points of the compass.  The figure described by the apex is an irregular oval or ellipse.  They sometimes remain stationary for a period.  In these several respects there is no difference, except in rapidity and extent, between their movements and the lesser ones performed by the large terminal leaflet whilst making its great oscillations.  The movements of the little leaflets are much influenced, as is