MOVEMENT IN PLANTS. 251 



(c) Fill a pipette or syringe with clear water, and let 

 drops fall on a leaf for about a minute: no movements 

 occur. 



(d) Fill the tube with water made inilky with powdered 

 chalk, instead of clean tap-water : movement occurs this 

 time. Another method is to cut off a few leaves and place 

 some in clear water, others in chalk-containing water, in 

 watch-glasses ; after a few minutes the leaves in the 

 chalky water show bending of the tentacles, those in the 

 pure water do not. 



(e) Strike or rub the gland of a tentacle with a gelatine- 

 coated rod : no movement occurs. 



353. Mode of Curvature of the Tentacles. Stimu- 

 late a tentacle with a piece of meat, or in some other way, 

 and carefully watch (using a lens) the process of curvature. 

 Bending may begin after 10 to 15 seconds, and a distinct 

 curvature, visible to the naked eye, may be seen in less than 

 a minute. The marginal tentacles will sometimes curve 

 through 270 in an hour. Note that the curvature is con- 

 fined to the base of the stalk, which bends sharply, while the 

 upper part remains straight and is carried over passively. 



354. Chemical stimuli generally act more vigorously than 

 mechanical stimuli, as shown by the greater rapidity of the move- 

 ment and the longer duration of the curvature. Many substances 

 (some useful, some injurious, some indifferent) in solution act as 

 stimuli. The tentacles will respond to a very dilute (0'02 per cent. ) 

 solution of ammonium phosphate. In experiments on chemical 

 stimulation, a simple plan is to place a cut Sundew-leaf in a watch- 

 glass containing the dissolved substance. 



355. Transmission of Stimulus. (a) Put a very 

 small fragment of raw meat on the centre of a leaf ; in about 

 24 hours nearly all the tentacles will have bent inwards. 

 Note that the short central ones, on which the meat was 

 placed, remain erect, but the stimulus is transmitted from 

 them outwards, so as to induce inward curvature of the 

 outer tentacles. 



(6) Place a fragment of meat on one of the long outer 

 tentacles. The latter bends inwards so as to carry the 



