SCABIOSA. [CHAP. 



of the stiff spines, which radiate on all sides from 

 the flower heads of this plant, the humble bees, by 

 which it is principally fertilised, can only touch the 

 florets with their heads, the two lobes often get in 

 one another's way, and according to Miiller it would 

 be a distinct advantage if one of them were absent. He 

 points out also that in fact one of them is sometimes 

 rudimentary, or even occasionally altogether absent. 

 This adaptation then, it would seem, has actually 

 commenced. 



Scabiosa arvensis is also proterandrous. About 50 

 florets are united in one head ; they increase in size 

 from the centre towards the circumference, while in 

 Sc. columbaria the outer row is considerably larger 

 than the rest, and in Sc. succisa they are nearly equal 

 in size. The honey is at the base of the tubular 

 florets, which, however, are more or less funnel- 

 shaped at the mouth, thus greatly facilitating the 

 access of insects. Not only are the florets proteran- 

 drous, but this is the case with the whole head ; for, 

 though the anthers come to maturity slowly and (as 

 a general rule) successively from the edge to the 

 centre, none of the stigmas emerge until the anthers 

 have all shed their pollen, when they rapidly come to 

 maturity. The male condition of the flower-head 

 lasts several days ; the stigmas, on the contrary, come 

 to maturity almost simultaneously. This difference 

 is obviously an advantage. From the length of time 

 during which the anthers are ripening, whenever 

 there is a sunny day, and the insects are abroad, they 

 are almost sure to find some anthers ready to dust 

 them with pollen. On the other hand, the stigmas 



