FUNCTION OF THE FLOWER 6 1 



Pollination 



136. A necessary preliminary to fertilization, however, is 

 pollination, which is brought about in many different and often 

 remarkable ways, all of which illustrate most clearly the nice 

 adaptations, or correlations, of plants with other organisms and, 

 in general, with their environment. 



137. It may first be noted that most flowers are so organized 

 as to effectually protect their pollen from wetting. Iliis means 

 in many cases merely that the flowers do not open except in 

 fair weather and then require only a few minutes or hours 

 for the accomplishment of pollination. Other flowers close 

 at night or during threatening weather, i. e., the petals assume 

 a position such as to protect the stamens from rain or dew. 

 In other cases the petals, some or all, are so disposed as to give 

 shelter to the stamens; and frequently the flowers are pendant, 

 so that the stamens are sheltered even when the petals are widely 

 spread. 



138. It is a well recognized biological principle that cross- 

 fertilization, i. e., fertilization by pollen from another plant of 

 the same species, results in more vigorous offspring than 

 does self-fertilization — fertilization resulting from the union of 

 elements of the same plant. Accordingly we find that plants 

 are so organized as to favor cross-fertilization. 



139. One of the most important agencies of pollination is 

 the wind. The plants for which the wind performs this service 

 all have small and inconspicuous flowers, i. e., the petals are 

 either wanting or, if present, are small and not brilliantly 

 colored. The pollen in such plants is light and powdery and is, 

 therefore, easily carried by the wind, sometimes to long dis- 

 tances. It is produced in great quantities and, as it is wafted 

 along on the wind in clouds, some grains are likely to fall upon 

 other flowers of the same species and be held there by the 

 adhesive stigma. 



