M CIKCUMNUTATION 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 basilaris (CaoteBB). — ^A seedling was carefully ob- 

 served, because considering its 

 Fig. 31. appearance and the nature of the 



mature plant, it seemed very un- 

 likely that either the hypocotyl or 

 cotyledons would circumnntate to 

 an appreciable extent. The coty- 

 ledons were well developed, being 

 ■9 of an inch in length, "22 in 

 breadth, and 'IS in thickness. 

 The almost cylindrical hypocotyl, 

 now bearing a minute spinous bnd 

 on its summit, was only -46 of an 

 inch in height, and '19 in dia- 

 ^ .■ I ■, • ■ .. • meter. The tracing (Fig. 31) shows 



OpuntM basilans : conjomt cir- ' j? i.i 



cumnutation of hypocotyl the Combined movement of the 



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



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



ledon, and movement traced . ^^ ,-, ni l f^ li r»ni.i 



during 66 h. on horizontal to 11 A M. onthe 31st. On the 29th 



glass. Movement of the ter- a nearly perfect ellipse was com- 



minal bead magnified about p]eted. On the 30th the hypocotyl 



30 times, here reduced to one- ■, n ^ 



third scale. Seedling kept in ^oved, from somo unknown cause, 



hot-house, feebly illuminated in the same general direction in a 



from above. 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 



<ictua! amount of movement of the bead at the end of the 



r 



