38 CIECUMNUTATION OF SEEDLINGS. Chap. L 



move both up and down and laterally ; but tbey do not rise up 

 at niglit in a conspicuous manner. 



Lupinus luteus (Leguminosai). — Seedlings of this plant were 

 observed because the cotyledons are so thick (about '08 of an 

 inch) that it seemed unlikely that they would move. Our 

 observations were not very successful, as the seedlings are 

 strongly heliotropic, and their circumnutation could not be 

 accurately observed near a north-east window, although they 

 had been kept during the previous day in the same position. 

 A seedling was then placed in darkness with the hypocotyl 

 secured to a stick; both cotyledons rose a little at first, and 

 then fell during the rest of the day ; in the evening between 

 5 and 6 p.m. they moved very slowly ; during the night one 

 continued to fall and the other rose, though only a little. The 

 tracing was not much magnified, and as the lines were plainly 

 zigzag, the cotyledons must have moved a little laterally, that 

 is, they must have circumnutated. 



The hypocotyl is rather thick, about "12 of inch; nevertheless 

 it circumnutated in a complex course, though to a small extent. 

 The movement of an old seedling with two true leaves partially 

 developed, was observed in the dark. As the movement was 

 magnified about 100 times it is not trustworthy and is not 

 given ; but there could be no doubt that the hypocotyl moved 

 in all directions during the day, changing its course 19 times. 

 The extreme actual distance from side to side through which 

 the upper part of the hypocotyl passed in the course of 14^ hours 

 was only -g^ of an inch ; it sometimes travelled at the rate of 

 ^ of an inch in an hour. 



Cucurbita ovifera (Cucurbitacess). — Eadicle : a seed which had 



Fig. 26. 



>n. 



Cucurbita ovifera : course followed by a radicle in bending geotropically 

 downwards, traced on a horizontal glass, between 11.25 A.M. and 10.25 

 P.M. ; the direction during the night is indicated by the broken line. 

 Movement of bead magnified 14 times. 



germinated on damp sand was fixed so that the slightly curved 

 radicle, which was only -07 inch in length, stood almost vertically 



