WIND - POLLINATED FLOWERS 79 



flower possesses both stamens and carpels, the pollen and the 

 stigmas are not ready for pollination at the same time. When 

 the stamens shed their pollen before the stigma is ready to 

 receive it, thfe flower is said to be proterandrous (e.g. Daisy- 

 family, Mallow). But when the stigma is ripe before the 

 anthers are able to dehisce, the flower is described as pro- 

 terogynous. 



(iii.) Sometimes the pollen has no fertilising effect on the 

 ovules of the same flower, so that when the- stigma receives 

 pollen from the same flower no seeds result (e.g. some Orchids). 



(iv.) The. relative arrangement of the parts of the flower, in 

 some cases, prevents the pollen reaching the stigma of the 

 same flower (see Pansy, on page 129; also see the long-styled 

 form of Primrose, on page 150). 



Cross-pollination by the aid of the wind — Wind-pollinated 

 flowers. — In the case of ordinary flowering plants with flowers 

 raised above ground or above the water, it is necessary for 

 pollen to be transported through the air if the flowers are to be 

 cross-pollinated. The pollen has no power to move unaided, 

 only rarely does the plant itself assist by throwing the pollen 

 violently (as in the Stinging Nettle) ; so that the pollen is 

 necessarily conveyed from one plant to another by the aid of 

 the wind or by the agency of animals. Flowers which are 

 cross-pollinated by the aid of the wind are described as wind- 

 pollinated flowers. Flowers which are cross-pollinated by the 

 agency of animals are animal-pollinated: in Britain the only 

 animals which are of importance in effecting the cross-pollination 

 of flowers are insects : hence we speak of insect-pollinated flowers. 



As examples of wind-pollinated flowers, we may mention 

 Hazels, Poplars, and Grasses (see pages 109-112, 182-184). In 

 regard to these wind-pollinated flowers, it will be noted that : 

 (i.) They are small, inconspicuous, and unscented. 

 (ii.) They have no nectaries. 



(iii.) Their pollen is powdery, and not sticky. 



(iv.) The anthers are attached to long filaments, and hang 

 freely out of the flowers, or are arranged in easily movable 

 inflorescences, so that the pollen is readily , shaken out by a 

 gentle breeze. 



(v.) The stigmas are well-developed, and often feathery 

 or thread-like, so that a large surface is exposed to receive 

 any pollen blown thither by the wind. 



