362 MODIFIED CIKCUMNUTATION. Chap. VU. 



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 64° 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 

 62° during nearly the whole night; at 10 and 11p.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. 61° F.) its inclination was still 

 less than before, and again less at 6.45 a.m ; by 7.40 am. 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 move- 

 ment was by jerks up to 1 a.m. (and possibly later) and again at 

 8.30 AM., though the temperature was only 61° to 62° 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 trifohate ; 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. gyram 

 (see former Fig. 148) must be considered as almost rudi- 

 mentary. They are also rudimentary in function, if this ex- 

 pression 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 my gardener observed (Oct. 13th) a plant in the hot-house 

 between 5 and 5.30 a.m.,, the temperature having been kept up 

 to 82° F., and found that all the leaflets were inclined, but he 

 saw no jerking movement until 6.55 a.m., by which time the 

 terminal leaflet had risen and was awake. Two days after- 

 wards (Oct. 15th) the same plant was observed by him at 

 4.47 A.M. (temp. 77° F.), and he found that the large terminal 

 ieaflets were awake, though not quite horizontal ; and the only 

 cause which we could assign for this anomalous wakefulness was 

 that the plant had been kept for experimental purposes during 



