252 MOVEMENT IN PLANTS. 



meat to the middle of the leaf ; then a stimulus is appa- 

 rently sent to the other peripheral tentacles, which begin 

 to curve inwards. Hence we can here distinguish between 

 movement caused by a direct stimulus and movement re- 

 sulting from a transmitted stimulus ; and transmission can 

 only be effected by means of the central tentacles. 



(c) Place two fragments of meat half-way between the 

 centre and the margin, at two opposite points : half of the 

 tentacles bend towards one centre of stimulation, and half 

 towards the other. 



356. Direct and Indirect Stimulation. Cut off the 

 glands of some of the marginal tentacles of a leaf, then 

 place a piece of meat on one of the remaining marginal 

 tentacles ; the results show that stimuli are transmitted 

 from the tentacles in the centre to those on the outside, 

 and that the stimulus acts on the motile portion of the 

 tentacle from below (a decapitated tentacle, though not 

 directly sensitive, reacts to a transmitted stimulus). 



When a tentacle is indirectly stimulated, the stimulus is 

 transmitted from above downwards to the motile region ; 

 in indirect stimulation, the transmission is from below up- 

 wards. In the former case it is always the outer side of 

 the tentacle which becomes convex (nastic curvature) ; in 

 the latter case the curvature is tropistic, being determined 

 by the direction from which the stimulus comes. 



IX. HAPTOTROPISM (CONTACT IRRITABILITY) OF STA- 

 MENS AND STIGMAS. 



357. Stamens of Berberis. Examine flowers of Bar- 

 berry, and note that there are several series of perianth 

 leaves, arranged in whorls of three. The inner six petals 

 have a nectary at their base ; each of the six stamens is 

 slightly attached at the base to one of these six petals. 

 The anthers open by two lateral valves near the top of the 

 anther. 



In the open flower, the stamens and petals are spread 



