STUDIES OF SEED-PLANTS 201 



boxes, keeping covered with mosquito-netting to ward off 

 insects, and then pollinating the flowers of the plants in one 

 or more pots, using a small brush or a feather to transfer 

 the pollen from stamens of the perfect to the pistillate flowers. 

 Perfect and pistillate plants for such an experiment can be 

 purchased from seed-dealers for about 30 cents per dozen, 

 postpaid, in autumn or spring. 



A second common adaptation against self-pollination is 

 found in some flowers in which the pollen and the stigma 

 of a flower are not mature (ready for pollination) at the same 

 time, but since the flowers open at different times it is possible 

 for insects to produce cross-pollination. 



Still another kind of protection against self-pollination is 

 illustrated by some flowers which have stamens much shorter 

 than the style so that pollen cannot fall upon the stigma of 

 the same flower, making pollination by insects necessary. 

 Also, there are other flowers (e.g., the bean and orchids) which 

 have their corollas peculiarly modified so that at the same 

 time they guard against self-pollination and favor cross- 

 pollination. 



194. Adaptations for Cross-pollination. The simplest of 

 the arrangements for cross-pollination is connected with 

 wind as an agency for carrying pollen. Great quantities 

 of light pollen are produced by many plants, and this floats 

 upon currents of air to the stigmas of other flowers. Indian 

 corn and pines are good examples. Many thousand species 

 of plants are known to be cross-pollinated by the wind. 



Some of the adaptations for cross-pollination by insects 

 are among the most remarkable structures in the plant 

 kingdom. The bean flower as an example has been described 

 in 75. Probably most flowers which, like that of bean 

 plant, are irregular in shape (not radially symmetrical) 

 are pollinated by insects. In some of the orchids (e.g., 

 lady-slipper) the flower has a peculiar sac surrounding the 

 anthers and the stigma, and through this insects must crawl 



