well known, by temperature.  This was clearly shown by immersing leaves with motionless leaflets in cold water, which was slowly raised to 103o F., and the leaflets then moved quickly, describing about a dozen little irregular circles in 40 m.  By this time the water had become much cooler, and the movements became slower or almost ceased; it was then raised to 100o F., and the leaflets again began to move quickly.  On another occasion a tuft of fine leaves was immersed in water at 53o F., and the leaflets were of course motionless.  The water was raised to 99o, and the leaflets soon began to move; it was raised to 105o, and the movements became much more rapid; each little circle or oval being completed in from 1 m. 30 s. to 1 m. 45 s.  There was, however, no jerking, and this fact may perhaps be attributed to the resistance of the water.

Sachs states that the leaflets do not move until the surrounding air is as high as 71o — 72o F., and this agrees with our

* ‘Die Period.  Beweg.,’ p. 39. [page 362]

experience on full-grown, or nearly full-grown, plants.  But the leaflets of young seedlings exhibit a jerking movement at much lower temperatures.  A seedling was kept (April 16th) in a room for half the day where the temperature was steady at 64o F., and the one leaflet which it bore was continually jerking, but not so rapidly as in the hot-house.  The pot was taken in the evening into a bed-room where the temperature remained at 62o during nearly the whole night; at 10 and 11 P.M. and at 1 A.M. the leaflet was still jerking rapidly; at 3.30 A.M. it was not seen to jerk, but was observed during only a short time.  It was, however, now inclined at a much lower angle than that occupied at 1 A.M.  At 6.30 A.M. (temp. 61o F.) its inclination was still less than before, and again less at 6.45 A.M.; by 7.40 A.M. it had risen, and at 8.30 A.M. was again seen to jerk.  This leaflet, therefore, was moving during the whole night, and the movement was by jerks up to 1 A.M. (and possibly later) and again at 8.30 A.M., though the temperature was only 61o to 62o F. We must therefore conclude that the lateral leaflets produced by young plants differ somewhat in constitution from those on older plants.

In the large genus Desmodium by far the greater number of the species are trifoliate; but some are unifoliate, and even the same plant may bear uni-and trifoliate leaves.  In most of the species the lateral leaflets are only a little smaller than the terminal one.  Therefore the lateral leaflets of D. gyrans (see Fig. 148) must be considered as almost rudimentary.  They are also rudimentary in function, if this expression may be used; for they certainly do not sleep like the full-sized terminal leaflets.  It is, however, possible that the sinking down of the leaflets between 1 A.M. and 6.45 A.M., as above described, may represent sleep.  It is well known that the leaflets go on jerking during the early part of the night; but