THE ORCHIDS OF NEW ENGLAND. 



59 



the top of the short column, opens in the bud. When the 

 flower is fully expanded, the pollen-masses are left quite free, 

 supported behind by the anther cells, and lying in front against 

 the concave back of the rostellum, with their upper pointed 

 ends resting on its crest. Each pollen-mass is almost divided 

 into two. The few elastic threads of the grains are weak, and 

 large masses of pollen can be broken off easily. The lip has two 

 basal lobes which curve up on each side, and these would com- 

 pel an insect to approach the rostellum straight in front. As 



Fig. 16. — Listera ovata. (From Muller.) 

 i. Side view of unfertilized flower : ov, ovary. 



2. Front view, after the pollen-masses, po, have been removed from the anther. The flat 

 rostellum (r) is bent forward and partly conceals the stigma (st). (Magnified one-half as much 

 as i.) », nectary. 



3. Pollen-masses adhering to a needle (greatly enlarged), c, cement. 



4. Grammoptera /wzn's, with a number of pollen-masses on its head. 



soon as the flower opens, if the exquisitely sensitive rostellum 

 be touched ever so lightly, a large drop of viscid fluid is instan- 

 taneously expelled, and, on exposure to the air, in two or three 

 seconds the drop sets hard, soon assuming a purplish brownish 

 tint. As the pointed tips of the pollen-masses lie on the crest 

 of the rostellum, they are always caught by the exploded drop." 

 This drop, then, does the work of a viscid disc for the pollen- 

 masses. 



" When the anther-cells open, the rostellum slowly curves 

 over the stigmatic surface, so that its explosive crest stands at 

 a little distance from the summit of the anther; and this is very 

 necessary, otherwise the summit would be caught by the viscid 



