MOVEMENT IN PLANTS. 253 



out, the anther of each stamen lying within the concave 

 upper portion of one of the petals. If the filament is 

 irritated it moves inwards, bringing the anther close to the 

 stigma. When a bee pokes its proboscis into the flower, 

 to reach the nectary at the base of each petal, the stamen 

 moves inwards, dusting the bee's head with the pollen. 



(a) Touch or stroke, with a mounted needle, different parts of the 

 stamen, and note that the anther is not sensitive. Localise the 

 sensitive region, by touching or stroking different parts of the outer 

 and the inner surfaces of the filament in different stamens. Note 

 that after the stamen has moved inwards it at once moves outwards 

 again, and in a few minutes has regained its original position. 



(6) Pull off some of the petals ; some of the stamens will come 

 away with a petal. Place each specimen (petal and stamen) on wet 

 blotting-paper under a watch-glass for about ten minutes, to recover 

 irritability. Then touch different parts of the stamen, using a lens 

 or dissecting stand, in order to locate the exact region of irritability. 



(c) Carefully detach a few open flowers, holding by a forceps just 

 below the flower and cutting with scissors just below the forceps. 

 Test the irritability of each flower by touching one of the stamens. 

 Then place the flowers floating in a watch-glass of water. Put the 

 watch-glass under a bell-jar or large inverted beaker, along with 

 another watch-glass containing a few drops of chloroform. 



Note that the flowers may be left for about ten minutes in this 

 atmosphere without injury. On removing the bell-glass and the 

 chloroform, note that the stamens are now quite insensible to 

 touches. 



Now leave the flowers exposed to fresh air, and test from time to 

 time. In from fifteen to thirty minutes the stamens will have 

 recovered their irritability. 



(d) Repeat the preceding experiment, but this time touch each 

 stamen immediately before placing the flower under the bell-jar. 

 Note that the stamens are able to recover their normal position in 

 spite of the chloroform. 



358. Stamens of Centaurea. Of special interest are 

 the movements of the stamens in Centaurea, e.g. the Corn- 

 flower. Examine the flower-head and note in the central 

 flowers the five anthers joined to form a tube, through 

 which the style grows after the flower opens. 



(a) Choose a flower which has just opened and in which some 

 pollen is exposed on the top of the anther-tube, though the style has 

 not yet protruded. With a camel-hair brush rapidly wipe off the 

 pollen, and note the extrusion of a worm-like mass of pollen from 



