Natural History 633 



small and light ; in the pine they are provided with two little blad- 

 ders, the better to float in the air. Conspieuous corollas are use- 

 less; they would even be a hindrance, catching the flying pollen 

 and preventing it reaching the stigma. The corolla has almost 

 entirely disappeared, the wind flower is small and inconspicuous. 

 The stamens hang far out of the flower on slender filaments, 

 dangling in the air, shaken by every gust. The stigmas, too, pro- 

 trude the crimson filaments, of the hazel, the feathers of the 

 plantain, the brushes which hang from the grass ear winnowing 

 the air for drifting pollen. 



Cross-pollination is secured by having male and female flow- 

 ers on separate plants, as in the poplar, or by ripening the stamens 

 and stigmas at different times, as in the grasses and plantains. 



Cross-Pollination : its Meaning 



Cross-pollination is of great importance to the progress of 

 evolution. By it the various new characters which are always 

 cropping up in different plants of a species are combined and 

 recombined, so that an infinite number of races is produced for 

 the sifting process of natural selection to work on. By cross- 

 breeding, in nature as in the garden, the advance of evolution is 

 speeded up. There are also cases where cross-pollination secures 

 a stronger progeny; the maize is a notable example, and one 

 thinks of Darwin's primroses. But it seems that this is due to 

 a re-arrangement of the hereditary complex, and not to any 

 essential stimulation. There are certainly many plants which get 

 on very well without cross-pollination, and there are many others 

 which are adapted to secure self-pollination if the cross fails. 



The abundant well-filled capsules which ripen among the 

 leaves of the sweet violet in autumn are not the product of the 

 spring flowers, so well adapted for insect visits but somehow so 

 seldom visited ; they come from flowers hidden among the leaves, 

 little green buds which never open, the stigmas of which receive 

 pollen from the stamens of the same flower. 



