Chap. VL SLEEP OF COTYLEDONS. 305 



or more than seven times as much. On the next night the 

 cotyledons occupied nearly the same position as before. On the 

 morning of the 24:th they stood horizontally, and at night were 

 60'^ above the horizon ; and so it was on the night of the 25th. 

 But four days afterwards (on the 29th), when the seedlings 

 were a week old, the cotyledons had ceased to rise at night to 

 any plain degree. 



Apium graveolens. — The cotyledons at noon were horizontal, 

 and at 10 p.m. stood at an angle of 61° above the horizon. 



J.actuca scarwla (Composite). — The cotyledons whilst young 

 stood sub-horizontally during the day, and at night rose so as 

 to be almost vertical, and some were quite vertical and closed ; 

 but this movement ceased when they had grown old and large, 

 after an interval of 11 days. 



Helianthus annuus (Compositse). — This case is rather doubtful ; 

 the cotyledons rise at night, and on one occasion they stood at 

 73° above the horizon, so that they might then be said to have 

 been asleep. 



Ipomoea ccerulea vel Pharhitis nil (ConvolvulacesB). — The coty- 

 ledons behave in nearly the same manner as those of the Anoda 

 and Nankin cotton, and like them gTow to a large size. "Whilst 

 young and small, so that their blades were from '5 to '6 of an 

 inch in length, measured along the middle to the base of the 

 central notch, they remained horizontal both during the middle 

 of the day and at night. As they increased in size they began 

 to sink more and more in the evening and early night ; and 

 when they had grown to a length (measured in the above 

 manner) of from 1 to 1'25 inch, they sank between 55° and 70° 

 beneath the horizon. They acted, however, in this manner only 

 when they had been well illuminated during the day. Never- 

 theless, the cotyledons have little or no power of bending 

 towards a lateral light, although the hypocotyl is strongly helio- 

 tropic. They are not provided with a pulvinus, but continue 

 to grow for a long time. 



Ipomoea purpurea (vel Pharhitis hispida). — The cotyledons 

 behave in all respects like those of /. ccerulea. A seedling witli 

 cotyledons '75 inch in length (measured as before) and 1-65 

 inch in breadth, having a small true leaf developed, was placed 

 at 5.30 P.M. on a klinostat in a darkened box, so that neither 

 weight nor geotropism could act on them. At 10 p.m. one coty- 

 ledon stood at 77° and the other at 82° beneath the horizon. 

 Before being placed in the klinostat they stood at 15° and 2'J° 



