38 GLANDULAR HAIRS. [chap. 



common but beautiful Cornflower {Centaurea cyanus) 

 is quite smooth, but the involucres forming the 

 flower-head are bordered with recurved teeth. In 

 this case, neither the stem nor the leaves show a trace 

 of such prickles. 



The same consideration throws light on the large 

 number of plants which are more or less glutinous, a 

 condition generally produced, as, for instance, in the 



Fig. 31 — Knautia di^sacifolia. 



flowers of the Gooseberry and of Linncsa borealis 

 (Fig. 32), by the presence of glandular hairs. Kerner 

 has called attention to a very interesting illustration 

 afforded by Polygonum amphibium. In this species 

 the stigma projects about one-fifth of an inch above 

 the flower, so that if ants could obtain access, they 

 would steal the honey without fertilising the flower; 

 a flying insect, on the contrary, alighting on the 

 flower, could scarcely fail to touch the stigma. 



