360 OUTLINES OF EVOLUTIONARY BIOLOGY 



poking its proboscis down to get at the honey, cannot fail to touch 

 them. Both male and female organs are very much modified in 

 structure, and united together to form the column (C). There 

 are three stigmas. Of these, however, only two (B, no) are 

 functional, and they lie at the back of the entrance to the 

 nectary. The third is specially modified to form a remarkable 

 organ known as the rostellum (B, C, ), which projects above the 



FIG. 182. Adaptation in the Flower of Orchis mascuJa in relation to Insect- 

 Fertilization. (From Weismann's " Evolution Theory.") 



A, side view of flower ; B, front view ; C, vertical section through the column ; J>, pol- 

 linia removed on the point of a pencil and still standing erect ; E, the same later on, 

 bent forwards. 



ei, entrance to nectary ; n, nectary ; na, stigmatic surface ; p, pollinia ; r, rostellum ; 

 Sm, honey guide ; sp, spur; st. ovary (twisted) ; U, lower lip of flower (labellum). 



other two in front of the mouth of the nectary. This rostellum, 

 or beak, consists of an exceedingly sticky body covered over by a 

 thin, membranous cap. The cap is so delicately adjusted that 

 the slightest touch is sufficient to push it down and expose the 

 sticky mass beneath, and it is so elastic that when the pressure 

 is removed it springs back into its original position and again 

 covers up the sticky substance. 



There is only one perfect anther, consisting of two sacs which 

 stand up above and behind the rostellum. Each sac contains a 

 single coherent mass of pollen grains instead of the usual loose, 



