Chap. I. OECHIS MASCULA. 11 



touch or the vapour of chloroform causes the exterior 

 membrane of the rostellum to rupture along certain 

 defined lines. 



At the same time that the rostellum becomes trans- 

 versely ruptured in front, it probably (for it was 

 impossible to ascertain this fact from the position of 

 the parts) ruptures behind in two oval lines, thus 

 separating and freeing from the rest of the exterior 

 surface of the rostellum the two little discs of mem- 

 brane, to which the two caudicles are attached exter- 

 nally, and to which the two balls of viscid matter 

 adhere internally. The line of rupture is thus very 

 complex, but strictly defined. 



As the two anther-cells are open longitudinally 

 in front from top to bottom, even before the flower 

 expands, it follows that as soon as the rostellum is 

 properly ruptured from the effects of a slight touch, 

 its lip can be depressed easily, and, the two little discs 

 of membrane being already separate, the two pollinia 

 now lie absolutely free, but are still embedded in their 

 proper places. So that the packets of pollen and the 

 caudicles still lie within the anther-cells ; the discs 

 still form part of the rostellum, but are separate : and 

 the balls of viscid matter still lie concealed within 

 the rostellum. 



Now let us see in the case of Orchis mascula (fig. 1) 

 how this complex mechanism acts. Suppose an insect 

 to alight on the labellum, which forms a good landing- 

 place, and to push its head into the chamber (see side 

 view. A, or front view, B), at the back of which lies the 

 stigma (s), in order to reach with its proboscis the end 

 of the nectary ; or, which does equally well to show 

 the action, push very gently a sharply-pointed common 

 pencil into the nectary. Owing to the pouch-formed 

 rostellum projecting into the gangway of the nectary, 



