446 The Physiology of Plants BOOK m 



apex produced by growth. Frank had previously (1868) 

 applied it to growth movements which result from external 

 influences. Baranetzky (1883) associated circumnutation 

 with the influence of gravity, saying that, in the absence 

 of the latter force, stems show simple nutation. Darwin, 

 in 1880, claimed to have shown that circumnutation is 

 universal in all growing organs. He investigated the rate 

 at which the movement progresses and determined it to 

 have a very wide range, a revolution being performed in 

 from two hours thirty minutes to three hours ten minutes 

 by Tamus, but only in from twenty-six hours thirty minutes 

 to forty-eight hours by Adhatoda. Wiesner criticized ad- 

 versely the wide distribution claimed for circumnutation 

 by Darwin, and said that many stems and leaves grow in 

 straight lines. He held that the movements of growing 

 organs are due mainly to two causes : (i) irregularity of 

 growth, depending on the want of absolute symmetry in 

 structure and on the component cells of the organ not all 

 possessing absolutely similar powers of growth ; and (2) the 

 fact that many factors involving opposing growth-tendencies 

 are brought to bear upon the growing organs, so that the 

 bendings are the expression of the resultant of many forces. 



Darwin held that though circumnutation is so closely 

 associated with growth, the two are not inseparable. He 

 showed in 1875 that though the tendrils of Eccremocarpus 

 and some of the internodes ceased circumnutating in one 

 and one-third hour when cooled to 24 C. they continued 

 to grow, though very slowly. 



A phenomenon akin to simple nutation was examined 

 by De Vries in 1874. It had long been known that in 

 organs which possess bilateral symmetry, whether anato- 

 mical or physiological, the growth of one surface is for 

 considerable periods in excess of that of the other. It can 

 readily be observed in the case of leaves, and occurs also 

 in certain tendrils. De Vries introduced the terms epinasty 



