26 CIKOUMNUTATION OF SEEDLINGS. Chap. 1 



placed only 1| inch from the vertical glass. At 6 40 a.m. it 

 stood horizontally; it then fell till 8.35, and then rose. Al- 

 together in the course of 12 h. it rose thrice and fell thrice, as 

 may be seen in Pig. 15. The great nocturnal rise of the coty- 

 ledons usually commences about 4 or 5 p.m., and on the following 

 morning they are expanded or stand horizontally at about 6.30 

 A.M. In the pre.sent instance, however, the great nocturnal rise 

 did not commence till 7 p.m.; but this was due to the hypocotyl 

 having from some unknown cause temporarily bent to the left 

 side, as is shown in the tracing. To ascertain positively that 

 the hypocotyl circumnutated, a mark was placed at 8.15 p.m. 

 behind the two now closed and vertical cotyledons ; and the 

 movement of a glass filament fixed upright to the top of the 

 hypocotyl was traced until 10.40 p.m. During this time it 

 moved from side to side, as well as backwards and forwards, 

 plainly showing circumnutation ; but the movement was small 

 in extent Therefore Fig. 15 represents fairly well the move- 

 ments of the cotyledons alone, with the exception of the one 

 great afternoon curvature to the left. 



Oxalis corniculata (var. cuprea).— The cotyledons rise at night 

 to a variable degree above the horizon, generally about 45° : 

 those on some seedlings between 2 and 5 days old were found 

 to be in continued movement all day long ; but the movements 

 were more simple than in the last two species. This may have 

 partly resulted from their not being sufBciently illuminated 

 whilst being observed, as was shown by their not beginning to 

 rise until very late in the evening. 



Oxalis (^BiophytuTn) sensHiva. — The cotyledons are highly re- 

 markable from the amplitude and rapidity of their movements 

 during the day. The angles at which they stood above or 

 beneath the horizon were measured at short intervals of time ; 

 and we regret that their course was not traced during the whole 

 day. "We will give only a few of the measurements, which were 

 made whilst the seedlings were exposed to a temperature of 22^° 

 to 244 ° C. One cotyledon rose 70° in 11 m. ; another, on a distinct 

 seedling, fell 80° in 12 m. Immediately before this latter fall 

 the same cotyledon had risen from a vertically downward to a 

 vertically upward position in 1 h. 48 m., and had therefore passed 

 through 180° in under 2 h. We have met with no other instance 

 of a circumnutating movement of such great amplitude as 180° ; 

 nor of such rapidity of movement as the passage through 80° in 

 12 m. The cotyledons of this plant sleep at night by rising 



