44 CIECUMNUTATION OF SEEDLINGS. Chap. I. 



their cotyledons for the first time during the day— one to the 

 extent of 90° and the other rather more; they remained in 

 nearly the same position until 10.40 p.m ; but by 7 a.m. on the 

 following morning the one which had been previously open to 

 the extent of 90° had its cotyledons vertical and completely 

 shut ; the other seedling had them nearly shut. Later in the 

 morning they opened in the ordinary manner. It appears 

 therefore that the cotyledons of this plant close and open at 

 somewhat different periods from those of the foregoing species 

 of the allied genera of Cucurbita and Lagenaria. 



Opuntia lasilaris (Cactese). — A seedling was carefully ob- 

 served, because considering its 

 appearance and the nature of the 

 mature plant, it seemed very un- 

 likely that either the hypocotyl or 

 cotyledons would circumnutate to 

 an appreciable extent. The coty- 

 ledons were well developed, being 

 •9 of an inch in length, '22 in 

 breadth, and "15 in thickness. 

 The almost cylindrical hypocotyl, 

 now bearing a minute spinous bud 

 on its summit, was only '45 of an 

 inch in height, and "19 in dia- 

 meter. The tracing (Fig. 31) shows 

 the combined movement of the 



Fig. 31. 



/ 



Opantia basilaris : conjoint cir- 

 cumnutation of hypocotyl 

 and cotyledon; filament hypocotyl and of one of the coty- 

 fixed longitudinally to coty- jedons, from 4.45 P.M. on May 28th 

 to 11 A.M. on the 31st. On the 29th 



ledon, and movement traced 

 during 66 h. on horizontal 

 glass. Movement of the ter- 

 minal bead magnified about 

 30 times, here reduced to one- 

 third scale. Seedling kept in 

 hot-house, feebly illuminated 

 from above. 



a nearly perfect ellipse was com- 

 pleted. On the 80th the hypocotyl 

 moved, from some unknown cause, 

 in the same general direction in a 

 zigzag line ; but between 4.30 and 

 10 P.M. almost completed a second 

 small ellipse. The cotyledons move only a little up and down : 

 thus at 10.15 P.M. they stood only 10° higher than at noon. The 

 chief seat of movement therefore, at least when the cotyledons 

 are rather old as in the present case, lies in the hypocotyl. The 

 ellipse described on the 29th had its longer axis directed at 

 nearly right angles to a line joining the two cotyledons. The 

 actual amount of movement of the bead at the end of the 



