496 



MODIFIED CIKOUMNUTATION. 



CUAP. X 



183. 



' 7:aiH.29'^ 



Ihen suddenly began to circumnutate. A partially etiolated 

 , and somewhat old hypocotyl 



^iS'.SSpm. pf g^ seedling cabbage (21 

 inches in height) was so 

 sensitive that when placed 

 at an angle of only 23' from 

 the perpendicularj it became 

 vertical in 33 minutes. As 

 ^^■^'1 1/ jt could not have been 



strongly acted upon by 

 ^P^^i- ;1>J 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 

 circnmnutating the line was 



a'SS'a.m.SS'!' L- 



SH(i mth]nris: apngeotropic movement 

 of hypocotyl from 19° beneath horizon 

 to a vertical position, with subsequent 

 circumuutation, 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 toone-thirdof original 

 Bcal :, 



