16 



CIKCUMNUTATION OF SEEDLINGS. CHAP. I. 



two cotyledons parallel to the window. It was thus left the 

 whole day so as to accommodate itself to the light. On the 

 following morning a filament was fixed to the midrib of the 

 larger and taller cotyledon (which enfolds the other and smaller 

 one, whilst still within the seed), and a mark being placed 

 close behind, the movement of the whole plant, that is, of the 

 hypocotyl and cotyledon, was traced greatly magnified on a ver- 

 tical glass. At first the plant bent so much towards the light 

 that it was useless to attempt to trace the movement ; but at 

 10 A.M. heliotropism almost wholly ceased and the first dot was 



Fig. 6. 







Brassica oleracea : conjoint circummitation of the hypocotyl and cotyledons 

 during 10 hours 45 minutes. Figure here reduced to one-half original 

 scale. 



made on the glass. The last was made at 8.45 P.M.; seventeen 

 dots being altogether made in this interval of 10 h. 45 m. (see 

 Fig. 6). It should be noticed that when I looked shortly after 

 4 P.M. the bead was pointing off the glass, but it came on again 

 at 5.30 P.M., and the course during this interval of 1 h. 30 m. has 

 been filled up by imagination, but cannot be far from correct. 

 The bead moved seven times from side to side, and thus de- 

 scribed 3s ellipses in 101 h. ; each being completed on an 

 average in 3 h. 4 m. 



On the previous day another seedling had been observed 

 under similar conditions, excepting that the plant was so 



