398 



GENERAL BOTANY 



In the young flowers the stamens are massed closely around 

 the pistils, with the anthers just below the stigmatic surfaces. 

 In the older flowers the outer stamens ripen first, and since the 



, , anthers are extrorse 



(that is, on the outer 

 abaxial surface of the 

 filament), the pollen 

 as it is shed is not 

 likely to reach the 

 stigmas without in- 

 sect aid. The dehis- 

 cence of the remaining 

 anthers, after the first, 

 is centripetal (that is, 

 from the outside of 

 the flower toward the 

 centrally located pis- 

 tils), which further 

 insures against self- 

 pollination. Insect 

 visitors are attracted 

 by the bright yellow 

 color of the petals 

 and by the abundant 

 nectar, which is se- 

 creted in two shallow 

 depressions on either 

 side of each ovary. 

 When they alight 

 upon the center of 

 the flower with pol- 

 len on the abdomen derived from other flowers, they effect 

 either close-pollination or cross-pollination, according to the 

 source of the pollen. Insects which pass from the outer border 

 of a flower across the center are likely to effect self-pollination. 

 The fruit is a many-seeded follicle which splits down the placen- 

 tal suture and liberates the seeds. 



Courtesy of American Magazine of Forestry, Washington, D. C. 



FIG. 249. Habit of the common buttercup 

 Photograph by Dr. R. W. Shufeldt 



