V.] CENTAUREA. 125 



the tubes of the florets are 7 10 mm., the cups 3 4^ 

 in length, each with five long, linear, lobes. The di- 

 vergence of the outer florets gives the whole head a 

 diameter of 20 30 mm. The hairs constituting the 

 pollen brush are not situated at the extremity of the 

 stigmas as in the preceding species, but form a ring 

 round the pistil at the spot where it bifurcates. When 

 the flower opens the pollen has been already shed into 

 the anther tube in the upper end of which it lies, 

 occupying the space between the anthers and the 

 pistil, and supported by the ring of hairs. If now 

 the flower remains untouched, after a while the stig- 

 matic lobes separate, and some of the pollen falls 

 on them. But if, as generally happens, an insect 

 alights on the flower, or if in any other way the tip of 

 the anthers is touched, immediately the stamens con- 

 tract, exposing the pollen, which is supported by the 

 stigmatic lobes. Gradually the pistil elongates, and 

 the stigmatic lobes separate ; by which time the 

 pollen has generally been all removed, as the flowers, 

 in consequence of their richness in honey, are much 

 frequented by insects. 



In C. nigra the outer florets are sometimes of the 

 same size as the rest, sometimes larger, and without 

 either stamens or pistils. In C. scabiosa this is always 

 the case. The tubes of the florets also are longer, 

 the cups deeper, and the honey less accessible, 

 in consequence of which it has fewer insect visitors. 

 Muller records only 21 against 48 in C. nigra. In 

 C. Cyanus also the ray florets are neuter. The con- 

 tractility of the stamens is very marked. In flowers 

 kept in a room, Muller observed that when touched, 



