302 MODIFIED CIBCUMNUTATION. Cii-U-. \1- 



the petioles diverged before it was light. The hypocotyl u' 

 slightly sensitive, so that if rubbed with a needle it benas 

 towards the rubbed side. In the case of Lepidium sativum, the 

 petioles of tl-.e cotyledons of young seedlings diverge during 

 the day and converge so as to touch each other during tno 

 night, by which means the bases of the tripartite blades are 

 brought into contact ; but the blades are so little raised that 

 they cannot be said to sleep. The cotyledons of several other 

 cruciferous plants were observed, but they did not rise sufficiently 

 during the night to be said to sleep. 



Oithago segetum (CaryophylleaB). — On the first day after the 

 cotyledons had burst through the seed-coats, they stood at noon 

 at an angle of 75° above the horizon ; at night they moved 

 upwards, each through an angle of 15° so as to stand quite 

 vertical and in contact with one another. On the second day 

 they stood at noon at 59° above the horizon, and again at 

 night were completely closed, each having risen 31°. On the 

 fourth day the cotyledons did not quite close at night. The 

 first and succeeding pairs of young true leaves behaved in 

 exactly the same manner. We think that the movement in this 

 case may be called nyctitropic, though the angle passed through 

 was small. The cotyledons are very sensitive to light and will 

 not expand if exposed to an extremely dim one. 



Anoda Wrightii (MalvaceaB). — The cotyledons whilst moderately 

 young, and only from -2 to '3 inch in diameter, sink in the 

 evening from their mid-day horizontal position to about 35° 

 beneath the horizon. But when the same seedlings were older 

 and had produced small true leaves, the almost orbicular 

 cotyledons, now -55 inch in diameter, moved vertically downwards 

 at night. This fact made us suspect that their sinking might 

 be due merely to their weight ; but they were not in the least 

 flaccid, and when lifted up sprang back through elasticity into 

 their former dependent position. A pot with some old seedUngs 

 was turned upside down in the afternoon, before the noc- 

 turnal fall had commenced, and at night they assumed in op- 

 position to their own weight (and to any geotropic action) an 

 upwardly directed vertical position. When pots were thus 

 reversed, after the evening fall had already commenced, the 

 sinking movement ajjpeared to be somewhat disturbed ; but all 

 their movements were occasionally variable without any apparent 

 cause. This latter fact, as well as that of the young cotyledons 

 not sinking nearly so much as the older ones, deserves notice. 



