380 CHAP. XXXIV. THE MECHANISM OF THE TWINING STEM 



glass was attached to the apex of the stem, to serve as an 

 index. The object of holding the stem erect was to eliminate 

 the action of lateral geotropism, so called. In spite of this, 

 the erected stem exhibited at rotational movement similar 

 to that of the stemwhen inclined. 



Torsional Activity of Different Internodes 



Experiment 203. — For the determination of the relative 

 activities of different internodes, suitable indices were 

 attached to the plant at the corresponding nodes. The fixed 

 circular scale serves for the measurement of the torsional 

 rotation. The index at the tip of the stem indicates the 

 total rotation. The difference between the angles described 

 by V and 1" measures the torsional rotation of the first 

 large internode. Similarly, the different activities of 

 successive internodes from top to bottom may be measured 

 (fig. 215). The results are given in Table XXXIX. 



Table XXXIX. — Rates of Rotation of Successive 



Internodes. 



Taking the position of the lowest index, which did not 

 move, as zero, the torsion of the first or highest internode 

 is 15°. Torsion rises to a maximum of 32° at the second 

 internode, where the rate of growth is also at its greatest. 

 The rate dechnes to 5° at the third, and to 3° at the fourth. 

 There is no rotation in the fifth internode, which was the 

 oldest. Old internodes occasionally exhibit a slight rota- 

 tional movement which is negative, i.e. opposite to that 

 of the normal. 



The results of the experiments just described prove that 



