THE MONOCOTYLEDONES 2097 



the animals after which they are named, a resemblance which may be more 

 than merely accidental. We may instance the case of Platanthera hifolia 

 which is pollinated by moths (Fig. 2032). The flowers exhale a scent 

 resembling that of a pink and it is particularly strong at night. The spur 

 is long and thin and half-filled with nectar (Fig. 2033), hence it can only be 



Fig. 2033. — Platanthera bifolia. A, Flower showing the cokimn. B, The column. Above, 

 the two half-anthers below which is the rostcllum, flanked by two glandular staminodes. 

 Beneath this is the stigma. C, The two poUinia with a common caudicle ending in a 

 retinaculum pad. {After Kmith.) 



reached by the proboscis of a moth. In probing the flower the poUinia 

 become attached to the head of the insect on either side of the proboscis. 

 As they are withdrawn they turn inwards and downwards by the con- 

 traction of the caudicles and cling to the base of the proboscis. When 

 another flower is visited therefore the pollinia come into contact with the 

 stigma and then they burst. 



Platanthera chlorantha (Fig. 2034) (the Large Butterfly Orchid) difl"ers 

 considerably from the last in its pollination mechanism. The flowers are 

 strongly fragrant and are greenish-white in colour. The spur is very long, 

 sometimes over 4 cm. in length. The caudicles end in two viscid discs or 

 retinacula, which are not covered by a rostellum. Two small pedicels arise 

 from the backs of the retinacula, to which the caudicles are attached at right 

 angles, the pollinia lying almost horizontally. The retinacula stand in front 

 of the stigmas and attach themselves to the insect's eyes. Then the pedicels 

 rotate so as to lower the pollinia to a position in which they will strike the 

 stigmas in the next flower visited. Darwin suggests that it may be advanta- 

 geous for the pollinia to become attached to the eyes because adhesion to 

 the hairy parts of the insect's body would be less efficient and the movements 

 of the pollinia, after they became attached, would be less precise if they 

 were adhering to the hairy surface of the body. 



