THE ANGIOSPERMAE 1283 



(e) Deceptive flowers 



(a) Deceptive nectar flowers Parnassia palustris 



(b) Deceptive nauseous flowers Paris qiiadrifolia 



(f) Hover Fly flowers Veronica chamaedrys 



iv. SmaU Insect Flowers Herminium monorchis 



I. Anemophily or Pollination by Wind 



The way in which wind could effect pollination was first described by 

 Sprengel in 1793. Plants which adopt this mechanism exhibit certain 

 peculiarities. In the first place the stigmas are often branched or are pro- 

 vided with brush-like or feathery outgrowths which are suitable for catching 

 wind-blown pollen. Further the pollen grains are usually smoothed- 

 walled, dry and light in weight so as to render them buoyant. 



In general, the flowers of wind-pollinated plants are devoid of showy 

 parts, calyx and corolla are either absent or are much reduced, and in the 

 case of monoecious inflorescences there may be a marked difference in the 

 form and arrangement of the male and female flowers. The male flowers 

 are usually more numerous than the female ones; they may be aggregated 

 into catkins or may form independent inflorescences of various forms. The 

 anthers are often loosely suspended from the tips of long filaments and may 

 hang outside the limits of the flowers. In some instances the individual 

 flowers are pendulous, allowing the whole flower to be swayed by the wind. 

 More rarely the floral parts are immobile, but the anthers are explosive. 



In wind-pollinated flowers the sexes are often separated, so that self- 

 pollination is entirely prevented, but in hermaphrodite flowers the anthers 

 usually mature well before the style is ripe for reception. 



There is often a direct correlation between the exposure to wind and the 

 composition of the flora of an area. It is found that in exposed, windy situa- 

 tions a larger proportion of the plants are wind-pollinated as compared with 

 more sheltered situations, which favour plants adapted to insect pollination. 



Some plants which are adapted to insect pollination may be at times 

 wind-pollinated. Examples of this are seen in such genera as Erica, Calluna 

 and Bartsia. In these flowers the corolla is so constructed that when the 

 flowers first open wind pollination is impossible, but nectar is secreted and 

 the flowers are normally pollinated by insects. Should insect pollination 

 fail, due, for example, to unfavourable weather conditions, the supply of 

 nectar may become exhausted before pollination has been effected. In such 

 cases the filaments subsequently elongate sufliciently to push the anthers out 

 beyond the limits of the corolla and when the pollen is liberated in this way 

 it can be carried by wind to the stigma of the same or a different flower. 



A similar adaptation is exhibited by some species of Cyclameti. In their 

 early state the flowers are adapted to insect pollination and the pollen grains 

 are covered with a sticky oil which ensures that they adhere to the body of a 

 visiting insect. If insect pollination fails the pollen becomes powdery, 

 the stickiness disappears and the grains become adapted to wind dispersal. 



