491) 



MODIFIED CIECUMNUTATION. 



Chap. X 



then suddenly began to circumnutate. A partially etiolated 



Fig. 183. ^isr.sSpM: 



sB:st 



'Ttam.Sg'* 



8°55'a,m.2a^ l^ 



Beta vulrjaris; apngeotropic movement 

 ofhypoootyl from 19° beneath horizon 

 to a vertical position, with subsequent 

 circumnatation, traced on a vertical 

 and on a horizontal glass-plate, from 

 8.28 A.M. Sept. 28th to 8.40 A.M. 29th. 

 Figure reduced to one-third of original 

 seal :. 



and somewhat old hypocotyl 

 of a seedling cabbage (21 

 inches in height) was so 

 sensitive that when placed 

 at an angle of only 23° from 

 the perpendicular, it became 

 vertical in 33 minutes. As 

 it could not have been 

 strongly acted upon by 

 apogeotropism in the above 

 slightly inclined position, 

 we expected that it would 

 have circumnutated, or at 

 least have moved in a zig- 

 zag course. Accordingly, 

 dots were made every 3 

 minutes; but, when these 

 were joined, the line was 

 nearly straight. After this 

 hypocotyl had become up- 

 right it still moved onwards 

 for half an hour in the same 

 general direction, but in a 

 zigzag manner. During the 

 succeeding 9 h. it circum- 

 nutated regularly, and de- 

 scribed 3 large ellipses. In 

 this case apogeotropism, 

 although acting at a very 

 unfavourable angle, quite 

 overcame the ordinary cir- 

 cumnutating movement. 



The hypocotyls of Beta 

 vulgaris are highly sensitive 

 to apogeotropism. One was 

 placed so as to project 19'^ 

 beneath the horizon ; it fell 

 at first a very little (see 

 Fig. 183), no doubt owing 

 to its weight ; but as it was 

 circumnutating the line was 



