Environment and Adaptation 231 



This usually ensures the pollination of the pistil of 

 a flower with pollen from stamens of corresponding 

 length, taken from another flower. 



FIG. 21 



A Recently opened flower of Pelargonium ; the stamens 

 are ready to discharge the pollen, but the stigma, st, is still 

 immature. 



B An older flower of Pelargonium, with the petals removed ; 

 the anthers have fallen, and the stigma is open and ready for 

 pollination. 



C Section of a young flower of Nasturtium; three of the 

 seven stamens have discharged their pollen; the others are 

 nearly ready to do so, but the pistil, st, is still immature. 



D Older flower ; all the stamens have discharged the pollen 

 and bent down ; the ripe pistil now occupies a position in front 

 of the open spur, where it will receive pollen brought from a 

 younger flower. 



Cross-pollination in Orchids. The orchids prob- 

 ably show the most extraordinary adaptations for 



