28 CIRCUMNUTATION OF SEEDLINGS. CHAP. I. 



Citrus aurantium (Orange) (Aurantiaceaj). The cotyledons 

 are hypogean. The circumnutation of an epicotyl, which at the 

 close of our observations was '59 of an inch (15 mm.) in height 

 above the ground, is shown in the annexed figure (Fig. 17), as 

 observed during a period of 44 h. 40 m. 



Fig. 17. 



Citrus aurantium : circumnutation of epicotyl with a filament fixed trans- 

 versely near its apex, traced on a horizontal glass, from 12.13 P.M. on 

 Feb. 20th to 8.55 A.M. on 22nd. The movement of the bead of the 

 filament was at first magnified 21 times, or 10^, in figure here given, 

 and afterwards 36 times, or 18 as here given ; seedling illuminated 

 from above. 



jfisculus liippocastanum (Hippocastaneae). Germinating seeds 

 were placed in a tin box, kept moist internally, with a sloping 

 bank of damp argillaceous sand, on which four smoked glass- 

 plates rested, inclined at angles of 70 and 65 with the 

 horizon. The tips of the radicles were placed so as just to 

 touch the upper end of the glass-plates, and, as they grew 

 downwards they pressed lightly, owing to geotropism, on the 

 smoked surfaces, and left tracks of their course. In the middle 

 part of each track the glass was swept clean, but the margins 

 were much blurred and irregular. Copies of two of these tracks 

 (all four being nearly alike) were made on tracing paper placed 

 over the glass-plates after they had been varnished ; and they 

 are as exact as possible, considering the nature of the margins 

 (Fig. 18). They suffice to show that there was some lateral, 

 almost serpentine movement, and that the tips in their down- 

 ward course pressed with unequal force on the plates, as 



