EXAMPLES OF POLLINATION 387 



horizontally, well beyond the mouth of the corolla, and the 

 moth, touching them as it sips nectar in its flight, receives 

 pollen ; the style, with the rounded stigma, is depressed out 

 of the insect's way. On the following night the stamens have 

 withered and sunk down, while the style has curved up so 

 that the stigma is now touched by the moths and is pollinated 

 from other flowers. On the second night the corolla is 

 yellower in colour, and its segments are rolled back. Knuth 

 suggests that moths may visit the newly opened flowers 

 first because of their brighter colour, but he was unable to 

 confirm this because of the rapidity of the insect's flight. 



In the yellow flag, Iris Pseiidacorus , the nectar lies in the 

 perianth tube to which access may be obtained by bees 

 under the broad stigma, one lobe of which lies over each 

 perianth segment. As the bee pushes in it rubs the 

 receptive flap of the stigma, and later brushes against the 

 stamens which are epipetalous within the tube. As it 

 retreats the bee pushes back the receptive flap so that this 

 does not receive pollen from the same flower. A form of 

 this plant has the stigmatal lobes so closely pressed to the 

 perianth that bees cannot push their way in ; it is pollinated 

 by syrphids. The bee flower is also visited by small insects 

 which drink nectar, but do not transfer pollen. 



In Linncea borealis, a moth flower, the bracts, inferior 

 ovary, and sepals are thickly clad with viscid, glandular hairs 

 which are said to prevent ants and other small crawling 

 insects from stealing the nectar. The flower has a peculiar 

 aromatic fragrance. The tube of the flower slants down- 

 wards so that protection of pollen and nectar from rain is 

 ensured. The stigma stands out from the mouth of the 

 corolla so that it is touched first ; the anthers lie further back, 

 and pollen can scarcely fall on the stigma. 



The floral mechanism of the orchids in all its variety 

 has been extensively investigated, particularly since the 

 publication of Darwin's monograph (1862). Except in 

 Cypripedium and its relatives the visiting insect brings off, 

 stuck to its head, the pollen of the single fertile stamen in 

 the form of the polHnia. As it flies the pollinia sink on 



