39 2 ORCHIS MASCVLA. PAKT n. 



of the two stalks of the pollinia, or granular masses, 

 are strongly attached to these little discs, or balls. 



At first the membrane forming the exterior surface of 

 the rostellum is continuous ; but as soon as the flower 

 opens, the slightest touch causes it to rupture in such a 

 manner as to set free from it, and from one another, 

 the little discs, while at the same time the anther cells 

 themselves split in a longitudinal direction from top to 

 bottom. In this state none of the 

 organs are changed ; they are merely 

 set free, and ready for change, yet 

 maintaining their normal positions. 

 The labellum, which is the largest 

 petal of the flower, lies on one side of 

 the nectary tube, and the rostellum 

 Fig. 76. Poiiinia of r- projects into it on the other ; hence, 

 ^ an insect alights on the labellum, 

 and pushes its head into the tube, 

 c , caudicie ; d, disc. j n or d er to reach the honey in the 

 nectary with its proboscis, it cannot fail to touch and 

 depress the rostellum (see fig. 76), so that one or both 

 of the viscid discs carrying the pollinia will stick to it, 

 and as the anther cells are open in front, when the in- 

 sect withdraws its head, one or both of the pollinia are 

 drawn out of their cells, and stick upright on it like 

 horns. In that position they never could fertilize any 

 blossom which the insect might afterwards visit; but 

 Mr. Darwin has shown that their position is changed by 

 a contrivance that is not surpassed in beauty in the whole 

 vegetable world. While a pollinium is upright on the 

 head of the insect, the little viscid disc which supports it 

 contracts on being exposed to the air, so as to cause the 

 pollinium to sweep through ninety degrees towards the 

 apex of the insect's proboscis, and this is accomplished 

 in about thirty seconds, the time an insect would take 

 to fly to another flower. The pollinium in this position 



