30 DARWINISM STATED BY DARWIN HIMSELF. 



the tenth chapter ; and under such circumstances the 

 same kind of evidence as that given in the chapter on 

 heliotropism showed in the plainest manner that apo- 

 geotropic and geotropic, and probably diageotropic move- 

 ments, are all modified forms of circumnutation. 



Different parts of the same plant and different species 

 are affected by gravitation in widely different degrees and 

 manners. Some plants and organs exhibit hardly a trace 

 of its action. Young seedlings, which, as we know, cir- 

 cumnutate rapidly, are eminently sensitive ; and we have 

 seen the hypocotyl of Beta bending upward through 109° 

 in three hours and eight minutes. The after-effects of 

 apogeotropism last for above half an hour ; and horizon- 

 tally-laid hypocotyls are sometimes thus carried tempo- 

 rarily beyond an upright position. The benefits derived 

 from geotropism, apogeotropism, and diageotropism, are 

 generally so manifest that they need not be specified. 

 With the flower-peduncles of Oxalis, epinasty causes them 

 to bend down, so that the ripening pods may be pro- 

 tected by the calyx from the rain. Afterward they are 

 carried upward by apogeotropism in combination with 

 hyponasty, and are thus enabled to scatter their seeds 

 over a wider space. The capsules and flower-heads of 

 some plants are bowed downward through geotropism, 

 and they then bury themselves in the earth for the pro- 

 tection and slow maturation of the seeds. This burying 

 process is much facilitated by the rocking movement due 

 to circumnutation. 



In the case of the radicles of several, probably of all 

 seedling plants, sensitiveness to gravitation is confined to 

 the tip, which transmits an influence to the adjoining 

 upper part, causing it to bend toward the center of the 

 earth. That there is transmission of this kind was proved 

 in an interesting manner when horizontally extended 



