OCCURRENCE AND DISTRIBUTION 21 



growing tip is projected from above on to a plane surface l . In flattened 

 organs, for mechanical reasons, the movement takes place mainly in 

 a definite plane, and for physiological reasons the same applies to dorsi- 

 ventral organs, and also to variation movements which in general are more 

 regular than nutation movements. During linear nutation the rapidity of 

 the return movement increases to a maximum and then gradually diminishes 

 up to the point of reversal. Secondary oscillations always occur, however, 

 and these are sometimes very pronounced. 



Pronounced circumnutation 2 , such as is shown by twining plants and 

 by many tendrils, usually maintains a constant direction. Nevertheless, in 

 the case of certain tendrils, the shoots of some leaf-climbers, and even of 

 a few twining plants, a periodic reversal of the circumnutation has been 

 observed 3 . In all cases the circumnutation results from the progression of 

 the more rapidly growing (epinastic) zone around the apical region. Hence 

 both the convex side and the front flank are continually changing, a 

 transverse section of the stem moving around the axis of revolution in the 

 same way that the earth would move around the sun if it had no daily 

 rotation. Under such circumstances no torsion is produced, but this is at 

 once shown if the same side always keeps in front. A hanging shoot 

 subjected to torsion will naturally show a revolving movement. 



In both young erect twining plants, and in the stems of older ones projecting 

 beyond the support, the entire growing zone is capable of nutation. The growing 

 and nutating zone of the Hop is 20 to 30 cm. and of Hqya carnosa up to 80 cm. 

 long 4 . In the case of tendrils the period of circumnutation is limited, and it stops 

 when growth ceases. Further the nutation only begins when the tendril has expanded 

 and attained a fair length 8 . Even in twining plants circumnutation does hot begin 

 until the seedling has attained a certain size, the first one or more internodes showing 

 no circumnutation 6 . 



Under favourable conditions a revolution is performed in one or two hours in 

 the case of Akebia quinata, Convolvulus sepium and Phaseolus vulgar is, whereas 

 Lonicera brachypoda requires five to six hours, and Adhatoda cydoniaefolia 24 to 

 48 hours 7 . The non-twining stems of Passiflora gracilis and the tendrils of Cobaea 



1 Cf. Darwin, Climbing Plants, 1875, P- IJ 3; Dutrochet, Ann. d. sci. nat., 1843, 2 e ser.,T. xx, 

 p. 314 ; Fritzsche, 1. c. 



2 Darwin (The Power of Movement in Plants, 1880, p. i) employed the term 'Circumnutation,' 

 Dutrochet (Ann. d. sci. nat., 1844, 3" se'r., T. u, p. 157) that of ' Revolutive (rotary) Nutation.' 



3 Darwin, The Movements and Habits of Climbing Plants, 1875, p. 34 seq.; O. Miiller, Cohn's 

 Beitrage z. Biologic, 1887, Bd. iv, p. 103 ; Wortmann, Bot. Ztg., 1887, p. 65 ; Baranetzsky, Die kreis- 

 formige Nutation u. das Winden d. Stengel, 1883, p. n. 



4 Darwin, The Movements and Habits of Climbing Plants, 1875, p. 3. 



5 Darwin, 1. c., p. 5 ; Wortmann, 1. c., p. 51 ; Fitting, Jahrb. f. wiss. Bot., 1903, Bd. xxxvin, 



P- 547- 



* Mohl, Ranken- und Schlingpflanzen, 1827, p. 104; Darwin, I.e., pp. 4, 26, 33; Schenck, 

 Beitrage z. Biologic u. Anatomic d. Lianen, 1892, I, p. 128. 



7 Darwin, 1. c., p. 26 ; Simons, Contrib. from the Bot. Lab. of Pennsylvania, 1898, Vol. u, p. 66. 



