SECT. II 



PHYSIOLOGY 



313 



iM 



organs which contain the reserve food material, as a rule stand erect. 

 With further growth the free end curves energetically to one side and 

 assumes a more or less oblique or horizontal position. At the same time 

 the inclined apex begins to revolve in circles like the hand of a watch. 

 This movement continues from the time of its inception as long as the 

 growth of the shoot lasts, and as a rule takes place in a definite direc- 

 tion. In the majority of twining 

 plants the circling movement as seen 

 from above is in the direction oppo- 

 site to that of the hands of a watch 

 (towards the left as we commonly 

 ^' express it). The Hop and the 

 Honeysuckle twine to the right, in 

 the direction of the hands of a watch. 

 In Boiviea voluhilis and Loasa lateritia 

 a rotation alternately to the right 

 and left has been observed. The 

 plants that circle to the left are also 

 left-handed climbers, i.e. the spiral 

 which their stems form (Fig. 233 I) 



mounts from the left to the right 

 and, as seen from above, against the 

 direction of the hands of a watch. 

 Similarly the jilants that circle to 



Fio. -iSS.— I, Sinistrorse shoot of rhnhitis. 

 II, Dextrorse shoot of Myrsiphiillina 

 asparagoides. 



Fig. 234. — Diagram of twining. 



the right are also right-handed twiners (Fig. 233 II). There is thus 

 an intimate connection between the circling movement and the twining. 



Tlie revolving movement can be made clearer by constructing a simple model. 

 Fasten a stiff-walled rubber tube at its base to an erect post, stick in its free end a 

 piece of lead pencil which is sufficiently heavy to bring tlie tube into a horizontal 

 position, and guide the point of the pencil in a circular direction opposite to that 

 of the hands of a watch (Fig. 23.:). If a coloured line is marked longitudinally on 

 the pencil it will be seen that this line during the revolving inovement rotates 



