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The Outline of Science 



stamens: they are of no use to the plant, and in fact they are 

 prevented from reaching the nectar by a circle of stiff hairs half- 

 way down the corolla tube, a palisade which they cannot 



penetrate. 



Such refinements are especially characteristic of those highly 

 specialised flowers which, like the sage, the orchids, the toad-flax, 

 and the broom, possess bilateral symmetry. This permits of the 

 formation of a landing-stage for heavy insects, and also leads to 

 adaptations which keep the visitor to one path. These adaptations 

 are well fitted to secure cross-pollination, which is advantageous 

 as regards both quantity and quality of seed. Insect-pollinated 

 flowers are not always bright. Thus the cuckoo-pint attracts flies 

 by a carrion stench, perhaps also by the lurid purple of the club of 

 its flowering axis. The flies are trapped among the female flowers 

 by a circle of hairs (modified stamens) inside the base of the 

 hood. They are liberated by the withering of the hairs, when 

 the staminate flowers are ripe; dusted with pollen, they then 

 escape to other plants. 



There are fruits, for example, the banana, which ripen with- 

 out pollination. There are even cases, like the brambles and the 

 hawkweeds, where the sexual process has been so completely 

 dispensed with that seeds are formed without fertilisation. But 

 usually pollination is a necessary preliminary to fruit and seed 

 production alike. Sometimes, when a plant is grown in a foreign 

 country, artificial pollination must be resorted to; the marrows 

 and peaches in our gardens and hot-houses are commonly pollin- 

 ated by hand. The red clover never set seed in New Zealand 

 till the humble-bee, to which it is adapted, was introduced. 



Wind Pollination 



In wind-pollinated plants the adaptations run on different 

 lines. The pollen is dust-like and is produced in enormous quan- 

 tities, for the chances of a grain borne in the air reaching the 

 stigma of a flower of its own species are remote. The grains are 



