1906.] 



Some Common Thistles. 



709 



remarkable structural and biological features, to which I hope 

 to refer in another place. The flowers have an odour very 

 strongly resembling that of honey, and quite distinct from 

 that of other species. In the thistles previously mentioned 

 each flower in the head possesses anthers which bear pollen, 

 and an ovary capable of producing seed. Moreover, in these 

 species seed is abundantly produced in each head of flowers.. 



Fig. 4. — Roots of Spear Thistle (second year plants). 



The creeping thistle has, however, two distinct types of flower- 

 head. In one of these the flowers have abortive anthers which 

 produce no pollen, while in the other pollen-bearing anthers 

 are present. These two kinds of flower-heads are always borne 

 on separate plants, and as each individual plant is capable of 

 spreading extensively below ground and sending up stems into 

 the air from its underground parts, distinct colonies bearing one 

 or other type of flower-head are sometimes met with occu- 

 pying comparatively large areas. A great many farmers 



