FLOWEKS AND INSECTS 
127 
usually two pollen-sacs, and stretched between them is the 
stigmatic surface. In this case, however, the pollen grains 
are not dry and powdery, but cling together in a mass, and 
cannot escape from the sac without being pulled out (see 
Fig. 133). The same sort of pollen is developed by the 
milkweeds. 
(2) Consecutive maturity. In these cases the pollen and 
3 
FIG. 133. A flower of an orchid (Habenaria). At 1 the complete flower is shown, 
with three sepals behind, and three petals in front, the lowest one of which has 
developed a long strap-shaped portion, and a still longer spur portion, the opening 
to which is seen at the 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 pollen sacs of 
the single stamen are seen in the centre of the flower, diverging downwards, 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 mass 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 
stick fast and the pollen masses are dragged out. In 3 a pollen mass (a) is 
shown sticking to each eye of a moth. Upon visiting another flower these pollen 
masses are thrust against the stigmatic surface and pollination is effected. After 
GRAY. 
