52 



CIECUMNUTATION OF SEEDLINGS. Chap. 1 



Fig. 39. 



morning, before it was light, they had risen to 59° above the 

 horizon; in the afternoon of the same day they were found 

 again horizontal. 



Beta vulgaris (Chenopodese).— The seedlings are excessively 

 sensitive to light, so that although on the first day they 

 were uncovered only during two or three 

 minutes at each observation, they all moved 

 steadily towards the side of the room 

 whence the light proceeded, and the trac- 

 ings consisted only of slightly zigzag lines 

 directed towards the light. On the next 

 day the plants were placed in a completely 

 darkeued room, and at each observation 

 were illuminated as much as possible from 

 vertically above by. a small wax taper. The 

 annexed figure (Fig. 39) shows the move- 

 ment of the hypocotyl during 9 h. under 

 these circumstances. A second seedling 

 was similarly observed at the same time, 

 and the tracing had the same peculiar 

 character, due to the hypocotyl often mov- 

 ing and returning in nearly parallel lines. 

 The movement of a third hypocotyl differed 

 greatly. 



We endeavoured to trace the movements 

 of the cotyledons, and for this purpose 

 some seedlings were kept in the dark, but 

 they moved in an abnormal manner ; they 

 continued rising from 8.45 a.m. to 2 p.m., 

 then moved laterally, and from 3 to 6 p.m. 

 descended ; whereas cotyledons which have been exposed all 

 the day to the light rise in the evening so as to stand verti- 

 cally at night; but this statement applies only to young 

 seedlings. For instance, six seedlings in the greenhouse had 

 their cotyledons partially open for the first time on the morning 

 of November 15th, and at 8.45 p.m. all were completely closed, 

 so that they might properly be said to be asleep. Again, on the 

 morning of November 27th, the cotyledons of four other seedlings, 

 which were surrounded by a collar of brown paper so that they 

 received light only from above, were open to the extent of 

 89°; at 10 p.m. they were completely closed; next morning 

 (November 28th) at 6.45 a.m., whilst H was still dark, two of them 



Beta vu'garig; circum- 

 nutation of hyi)o- 

 cotyl, with filament 

 fixed obliquely a- 

 cross its summit, 

 traced in darkness 

 on horizontal glass, 

 from 8.25 a.m. to 

 5.30 P.M. Nov. 4th. 

 Movement of bead 

 magnified 23 times, 

 here reduced to one- 

 third of original 

 scale. 



