CHAP. I. GITHAGO. 21 



two or three minutes whilst a glass filament was fixed vertically 

 to the hypocotyl ; it was then again placed in darkness for half 

 an hour and afterwards observed by light passing through 

 bichromate of potassium. The point, oscillating as usual, 

 crossed five divisions of the micrometer (i.e. y^ inch) in 

 1 m. 30 s. The seedling was then left in darkness for an hour, 

 and now it required 3m. 6s. to cross one division, that is, 

 15 m. 30 s. to have crossed five divisions. Another seedling, 

 after being occasionally observed in the back part of a northern 

 room with a very dull light, and left in complete darkness for 

 intervals of half an hour, crossed five divisions in 5 m. in the 

 direction of the window, so that we concluded that the move- 

 ment was heliotropic. But this was probably not the case, for 

 it was placed close to a north-east window and left there for 

 25 m., after which time, instead of moving still more quickly 

 towards the light, as might have been expected, it travelled 

 only at the rate of 12 m. 30 s. for five divisions. It was then 

 again left in complete darkness for lh., and the point now 

 travelled in the same direction as before, but at the rate of 

 3 m. 18 s. for five divisions. 



We shall have to recur to the cotyledons of the cabbage in a 

 future chapter, when we treat of their sleep-movements. The 

 circumnutation, also, of the leaves of fully-developed plants 

 will hereafter be described. 



Fig. 11. 



Githago seyetum: circumnutation of hypocotyl, traced on a horizontal 

 glass, by means of a filament fixed transversely across its summit, from 

 8.15 A.M. to 12.15 P.M. on the following day. Movement of bead of 

 filament magnified about 13 times, here reduced to one-half the original 

 scale. 



Githago segetum (Caryophylleae). A young seedling was dimly 

 illuminated from above, and the circumnutation of the hypo- 



