MOVEMENTS OF SEEDLINGS. 45 



part bends from the light; but when excited by 

 gravitation the same part bends towards the centre 

 of gravity. In almost every case we can clearly 

 perceive the final purpose or advantage of the sev- 

 eral movements. Two, or perhaps more, of the 

 exciting causes often act simultaneously on the tip, 

 and one conquers the other, no doubt in accordance 

 with its importance for the life of the plant. The 

 course pursued by the radicle in penetrating the 

 ground must be determined by the tip; hence it 

 has acquired such diverse kinds of sensitiveness. 

 It is hardly an exaggeration to say that the tip of 

 the radicle, thus endowed, and having the power 

 to direct the movements of the adjoining parts, 

 acts like the brain of one of the lower animals ; 

 the brain being seated within the anterior end of 

 the body, receiving impressions from the sense- 

 organs, and directing the several movements." l 



In seedlings, such as the Bean (Fig. 8), and 

 Squash (Fig. 9), which lift their cotyledons above 

 the ground, the stem below the cotyledons, called 

 by Darwin the hypocotyl, is the first to break out 

 from the seed-coats after the protrusion of the rad- 

 icle. In seedlings, such as the Pea, where the 



1 p. 572. This is cojisjtfered aji extravagant .assumption by Sachs 

 .9,nd others. 



