194 BERBEKIS. [CH. VIII 



(242) Berberis (Mahonia) aquifolium: irritable 

 stamens^ 



The flowers do not easily lose their irritability; cut 

 twigs in water may be used, or even isolated flowers, if 

 only moderate care is used to prevent them withering. 



In the condition of repose the anthers lie in the bifid 

 hoods of the petals : when the filaments are irritated they 

 curve inwards, bringing the anthers close up to the 

 stigma. To localise the irritable part, the anther should 

 first be gently stroked on both faces with a dissecting 

 needle or mounted bristle. No movement occurs, but the 

 filament springs in at once when touched on its inner face 

 just below the anther. The outer surface of the filament 

 is not sensitive except at its extreme base. To make 

 sure of this the petals should be dissected off, an 

 operation which requires a little care, and the specimen so 

 prepared should be placed on wet filter-paper under a 

 watch-glass for 10 minutes to recover irritability. Under 

 a simple lens it is now easy to touch the filament in any 

 part. 



The filaments apparently begin to recover from the 

 eff'ect of a touch at once, at any rate a considerable 

 amount of return towards the resting position is visible 

 in 1 or 2 minutes, and in 5 or 10 minutes recovery is 

 complete. 



The stamens may be irritated separately, no trans- 

 mission fi-om one to the next takes place. By applying 



' Some of the larger flowered species are more convenient to work 

 with. 



