40 INTERRELATIONS OF PLANTS AND ANIMALS 



this pollen to the stigma of another flower. In this way pollen 

 is carried by the insect to another flower of the same kind. This 

 is known as cross-pollination. By pollination we mean the transfer 

 of pollen from an anther to the stigma of a flower. Self-pollination is 

 the transfer of pollen from the anther to the stigma of the same flower; 

 cross-pollination is the transfer of pollen from the anthers of one 

 flower to the stigma of another flower on the same or another plant 

 of the same kind. 



History of the Discoveries regarding Pollination of Flowers. - 

 Although the ancient Greek and Roman naturalists had some vague 



ideas on the subject of pollina- 

 tion, it was not until the first 

 part of the nineteenth century 

 that a book appeared in which 

 a German named Conrad 

 Sprengel worked out the facts 

 that the structure of certain 

 flowers seemed to be adapted 

 to the visits of insects. Cer- 

 tain facilities were offered to 

 an insect in the way of easy 

 foothold, sweet odor, and 

 especially food in the shape of 

 pollen and nectar, the latter a 

 sweet-tasting substance manu- 

 factured by certain parts of the 

 flower known as the nectar 

 glands. Sprengel further dis- 

 covered the fact that pollen 

 could be and was carried by 

 the insect visitors from the 

 anthers of the flower to its 

 stigma. It was not until the middle of the nineteenth century, 

 however, that an Englishman, Charles Darwin, applied Sprengel's 

 discoveries on the relation of insects to flowers by his investiga- 

 tions upon cross-pollination. The growth of the pollen on the 

 stigma of the flower results eventually in the production of seeds, 



A wild orchid, a flowor of tlu typ^ from 

 which Charles Darwin worked out his 

 theory of cross-pollination by insects. 



