CHAP. X MOVEMENTS EXCITED BY GRAVITATION. 493 



CHAPTER X. 



MODIFIED CIRCUMNUTATION : MOVEMENTS EXCITED BY GRAVITATION. 



Means of observation ApogeotropLm Cytisus Verbena Beta 

 Gradual conversion of the movement of circumnutation into apogeo- 

 tropism in Rubus, Lilium, Phalaris, Avena, and Bra.-sica Apogeo- 

 tropism retarded by heliotropism Effected by the aid of joints 

 or pulvini Movements of flower-peduncles of Oxalis General 

 remarks on apogeotropism Geotropism Movements of radicles 

 Burying of seed-capsules Use of process Trifolium subterraneum 

 Arachis Amphicarpsea Diageotropism Conclusion. 



OUK object in the present chapter is to show that 

 geotropism, apogeotropism, and diageotropism are mo- 

 dified forms of circumnutation. Extremely fine fila- 

 ments of glass, bearing two minute triangles of paper, 

 were fixed to the summits of young stems, frequently 

 to the hypocotyls of seedlings, to flower-peduncles, 

 radicles, &c., and the movements of the parts were 

 then traced in the manner already described on 

 vertical and horizontal glass-plates. It should be 

 remembered that as the stems or other parts become 

 more and more oblique with respect to the glasses, the 

 figures traced on them necessarily become more and 

 more magnified. The plants were protected from light, 

 excepting whilst each observation was being made, and 

 then the light, which was always a dim one, was 

 allowed to enter so as to interfere as little as possible 

 with the movement in progress ; and we did not detect 

 any evidence of such interference. 



When observing the gradations between circumnu- 



