48 



CIRCUMNUTATION OF SEEDLINGS. CHAP. I 



3.45 A.M. When again looked 

 Fig. 35. 



Ipomcea ccerulea : circumnutation of 

 cotyledon, traced on vertical glass, 

 from 6.10 A.M. June 21st to 6.45 

 A.M. 22nd. Cotyledon with petiole 

 1'6 inch in length, apex of blade 

 4'1 inch from the vertical glass; 

 so movement not greatly mag- 

 nified ; temp. 20 C. 



at, at 6.10 A.M. (21st), it had 

 fallen largely. A new tracing 

 was now begun (see Fig. 35), 

 and soon afterwards, at 6.42 

 A.M., the cotyledon had risen a 

 little. During the forenoon it 

 was observed about every 

 hour; but between 12.30 and 

 6 P.M. every half-hour. If the 

 observations had been made at 

 these short intervals during the 

 whole day, the figure would 

 have been too intricate to have 

 been copied. As it was, the 

 cotyledon moved up and down 

 in the course of 16 h. 20 m. (i.e. 

 between 6.10 A.M. and 10.30 

 P.M.) thirteen times. 



The cotyledons of this seed- 

 ling sank downwards during 

 both evenings and the early 

 part of the night, but rose 

 during the latter part. As this 

 is an unusual movement, the 

 cotyledons of twelve other seed- 

 lings were observed ; they stood 

 almost or quite horizontally at 

 mid-day, and at 10 P.M. were 

 all declined at various angles. 

 The most usual angle was be- 

 tween 30 and 35; but three 

 stood at about 50 and one at 

 even 70 beneath the horizon. 

 The blades of all these cotyle- 

 dons had attained almost their 

 full size, viz. from 1 to 1 inches 

 in length, measured along their 

 midribs. It is a remarkable 

 fact that whilst young that 

 is, when less than half an inch 

 in length, measured in the 

 same manner they do not sink 



