212 CENTAUREA. [CH. VIII 



sort the fixed lamella is forced to be more or less horizontal 

 and is perfectly free from contact, even at the base, with 

 the opposite lobe. 



(245) Stamens of Centaurea cyanus. 



We use the garden form of this species for demon- 

 strating the fact that the stamens are irritable 1 . 



Select a floret which has expanded but has not 

 extruded its style, place it on a piece of wet filter-paper 

 and under a simple lens split the floret at the swollen 

 part of the corolla- tube, which can then be opened wide 

 enough to give a view of the filaments. Cover the 

 preparation with an inverted watch-glass and leave it for 

 15 minutes, to recover from the effects of the operation. 

 If the filaments are now gently touched, a writhing 

 contraction is plainly seen. The anther tube may in this 

 way be made to swing over first to one side, then to 

 another, as the filaments are made to contract on the 

 corresponding sides. 



To see the extrusion of pollen another flower must be 

 used : the best plan is to remove the pollen at the free 

 end of the anther-tube \\ith a camel-hair brush. If this 

 is done with a rapid touch, the filaments are irritated and 

 a ribbon of pollen emerges immediately after the blow. 



(246) Phycomyces : curvature towards iron. 



Elfving has shown that the sporangiferous hyphse of 

 Phycomyces nitens curve towards iron. It is only necessary 



1 Pfeffer employed C. jacea and Cynara scolymus. See his Physio- 

 logische Untersuchungen, 1873, p. 80. 



