Chap. X. APOGEOTEOPISM. 503 



BO placed that the end of the filament stood beneath the 2-inch 

 object glass of a microscope with an eye-piece micrometer, each 

 division of which equalled -g^ of an inch. The end of the fila- 

 ment was repeatedly observed during 6 h., and was seen to be 

 in constant movement ; and it crossed 5 divisions of the micro- 

 meter (tso inch) in 2 h. Occasionally it moved forwards by 

 jerks, some of which were yoVo 'noh in length, and then slowly 

 retreated a little, afterwards again jerking forwards. These 

 oscillations were exactly like those described under Brassica 

 and Dionsea, but they occurred only occasionally. We may 

 therefore conclude that this moderately old joint was continually 

 circumnutating on a small scale. 



Alopecuriis pratensis.—Ayoung plant, 11 inches in height, with 

 the flower-head protruded, but with the florets not yet expanded, 

 had a glass filament fixed close above the second joint, at a 

 height of only 2 inches above the ground. The basal internode, 

 2 inches in length, was cemented to a stick to prevent any 

 possibility of its circumnutating. The extremity of the filament, 

 which projected about 60° above the horizon, was often observed 

 during 24 h. in the same manner as in the last case. Whenever 

 looked at, i-t was always in movement, and it crossed 30 divisions 

 of the micrometer (J^ inch) in 3i h. ; but it sometimes moved 

 at a quicker rate, for at one time it crossed 5 divisions in li h. 

 The pot had to be moved occasionally, as the end of the filament 

 travelled beyond the field of vision ; but as far as we could 

 judge it followed during the daytime a semicircular course ; 

 and it certainly travelled in two different directions at right 

 angles to one another. It sometimes oscillated in the same 

 manner as in the last species, some of the jerks forwards being 

 as much as y^oo of an inch. We may therefore conclude that 

 the joints in this and the last species of grass long continue to 

 circumnutate ; so that this movement would be ready to be 

 converted into an apogeotropic movement, whenever the stem 

 was placed in an inclined or horizontal position. 



Movements of the Flower-peduncles of Oxalis carnosa, due to 

 apogeotropism and other forces. — The movements of the main 

 peduncle, and of the three or four sub-peduncles which each 

 main peduncle of this plant bears, are extremely complex, and 

 are determined by several distinct causes. Whilst the flowers 

 are expanded, both kinds of peduncles circumnutate about the 

 sanrc spot, as we have seen (Fig 91) in the fourth chapter. 

 But soon after the flowers have begun to wither the sub- 

 33 



