II COMPOSlTJi 245 



feathery. The thistles are more or less effectively pro- 

 tected by the spiny leaves and flower-heads. There are 

 eleven British species. Several of them hybridise freely. 

 The species with a feathery pappus are often placed 

 under another genus, Cnicus. 



0. acanthoides. — In this species the leaf surface is 

 supplemented by green wings which run down from the 

 base of the leaves. Similar wings occur in C. nutans, 

 C. pycnoceplialus, C. lanceolatus, C. palustris, and 

 C. arvensis. 



Carlina 



Receptacle with scales. Florets all tubular and 

 complete. The white inner bracts take the place of the 

 ray florets and make the flower-heads very conspicuous ; 

 they also seem to protect the florets, as they close over 

 in bad weather and at nio-ht. The outer ones are very 

 prickly, the inner ones smooth and shining. 



C. vulgaris is the only British species. The leaves 

 are green above, cottony below. 



Onopordon 



Receptacle with scales. Florets tubular, complete. 



0. Acanthium. — The filaments are sensitive. The 

 plant is covered with a loose cottony wool. This is the 

 so-called Scotch thistle, and, though not a Scotch plant, 

 has been adopted by heralds as the special emblem of 

 that country. 



In most Composites the pollen is pushed out of the 

 anther tube by the growth of the pistil, as already 

 described (p. 232). In Onopordon and Centaurea a 

 different plan is adopted. The filaments of the stamens 

 are sensitive ; they protect the pollen, but if touched 

 by an insect, rapidly contract, carrying down, of course, 

 the anthers with them, and as the stigma is stationary 

 the pollen is squeezed out. This arrangement is 

 perhaps connected with the fact that in Onopordon the 

 heads are unable to close up. 



