498 



MODIFIED CIECUMNUTATION. 



Chap. X 



Fig. 184 



ii 



seen how gradually circumnutation becomes changed into apogoo- 

 tropism, under circumstances to be specified 

 in each instance. 



Eubus idceus (hybrid). — A young plant, 11 

 inches in height, growing in a pot, was placed 

 horizontally; and the upward movement was 

 traced during nearly 70 h. ; but the plant, 

 though growing vigorously, was not highly 

 sensitive to apogeotropism, or it was not 

 capable of quick movement, for during the 

 above time it rose only 67°. We may see in 

 the diagram (Fig. 184) that during the first 

 day of 12 h. it rose in a nearly straight line. 

 When placed horizontally, it was evidently 

 circumnutating, for it rose at first a little, 

 notwithstanding the weight of the stem, and 

 then sauk down ; so that it did not start on 

 its permanently upward course until 1 h. 

 25 m. had elapsed. On the second day, by 

 which time it had risen considerably, and 

 when apogeotropism acted on it with somewhat 

 less power, its course during 15 i h. was clearly 

 zigzag, and the rate of the upward movement 

 was not equable. During the third day, also 

 of 15^ h., when- apogeotropism acted on it 

 with still less power, the stem plainly circum- 

 nutated, for it moved dtiring this day 3 times 

 up and 3 times down, 4 times to the left and 

 4 to the right. But the course was so complex 

 that it could hardly be traced on the glass. 

 We can, however, see that the successively 

 formed irregular ellipses rose higher and 

 higher. Apogeotropism continued to act on 

 the fourth morning, as the stem was still 

 rising, though it now stood only 23° from the 

 perpendicular. In this diagram the several 

 stages may be followed by which an almost 

 rectilinear, upward, apogeotropic course first 

 becomes zigzag, and then changes into a 

 circumnutating movement, with most of the 

 successively formed, irregular ellipses directed 

 upwards. 

 falium aurdfum.— A -plant 23 inches in height was placed 



