506 MODIFIED CIECUMNUTATION. CHAP. X. 



In order to trace this upward movement, a filament was fixed 

 to a sub-peduncle bearing a capsule nearly ripe, which was 

 beginning to bend upwards by the two means just described. Its 

 course was traced (see C, Fig. 188) during 53 h., by which time 

 it had become nearly upright. The course is seen to be strongly 

 zigzag; together with some little loops. We may therefore con- 

 clude that the movement consists of modified circumnutation. 



The several species of Oxalis probably profit in the following 

 manner by their sub-peduncles first bending downwards and 

 then upwards. They are known to scatter their seeds by the 

 bursting of the capsule; the walls of which are so extremely 

 thin, like silver paper, that they would easily be permeated by 

 rain. But as soon as the petals wither, the sepals rise up and 

 enclose the young capsule, forming a perfect roof over it as 

 soon as the sub-peduncle has bent itself downwards. By its 

 subsequent upward movement, the capsule stands when ripe 

 at a greater height above the ground by twice the length of the 

 sub-peduncle, than it did when dependent, and is thus able 

 to scatter its seeds to a greater distance. The sepals, which 

 enclose the ovarium whilst it is young, present an additional 

 adaptation by expanding widely when the seeds are ripe, so as 

 not to interfere with their dispersal. In the case of Oxalis 

 acetosella, the capsules are said sometimes to bury themselves 

 under loose leaves or moss on the ground, but this cannot occur 

 with those of 0. carnosa, as the woody stem is too high. 



Oxalis acetosella. The peduncles are furnished with a joint in 

 Fig.-189. 



Oxalis acetosella : course pursued by the upper part of a peduncle, whilst 

 rising, traced from 1 1 A.M. June 1 st to 9 A.M. 3rd. Figure here re- 

 duced to one-half of the original scale. 



the middle, so that the lower part answers to the main peduncle, 



