FLOWERS AND INSECTS 



127 



usually two pollen-sacs, and stretclied between them is the 

 stigmatic surface. In this case, however, the pollen grains 

 are not dry and powdery, but cling togctlier in a mass, and 

 cannot escape from the sac without being pulled out (see 

 Fig. 133). The same sort of pollen is developed Ijy the 

 milkweeds. 



(2) Consecutive mahcinty. — In these cases the pollen and 



Fig. 133. A flower of an orchid (Flabenaria). At 1 the complete flower is shown, 

 with three sepals Ijehind, and tiireo petals in front, the lowest one of which has 

 developed a long strap-shaped portion, and a still longer spur portion, the ripening 

 to which is seen at tlie base of the strap. At the bottom of this long spur is the 

 nectar, which is reached by the long proboscis of a moth. The two polk^n sacs of 

 the single stamen are seen in the centre of tlie flower, diverging down\\'ards, and 

 between them stretches the stigma surface. The relation between pollen sacs and 

 stigma surface is more clearly shown in 2. Within each pollen sac is a mnss of 

 sticky pollen, ending below in a sticky disk, which may be seen in 1 and 2. When 

 the moth thrusts his proboscis into the nectar tube, his head is against the stig- 

 matic surface and also against the disks. When he removes his head the disks 

 Btick fast and the pollen masses are dragged out. In 3 a pollen mass (a) is 

 shown sticlving to each eye of a moth. Upon visiting another flower tliese pollen 

 masses are thrust against the stigmatic surface and pollination is effected.— After 

 Gray. 



