170 SUNFLOWER. 



g. The hairs by which they are held. 



h. Try to determine whether these flowers are necessarily 

 self-pollinated, by finding whether pollen is ready to be 

 shed at the time the stigma is ripe, and by finding 

 whether the position of parts favors self-pollination or 

 cross-pollination. 



i. Draw the disk -flowers. 



ANNOTATIONS. 



In the lowest group of Angiosperms the flowers are 

 hypogynous, the floral organs are numerous, and the 

 flowers are scattered. In higher groups there is a con- 

 stant tendency toward perigynous (corolla around the 

 ovary) and epigynous (corolla above or upon the ovary) 

 flowers, and also toward a relatively small and regular 

 number of floral organs in each set. Some groups 

 lower than Compositae have attained epigyny and definite 

 numbers, and the Umbelliferae (one of the highest family 

 of Dicotyledons) have approached the Composite inflor- 

 escence, but this feature in its highest expression is the 

 distinguishing characteristic of this great group. The 

 form of inflorescence makes possible the production of 

 many flowers upon a relatively small area. 



The structures of the plant body of Helianthus indicate 

 some of the excellent adaptations to environment so 

 common in Compositae, though by no means peculiar to 

 this family. The plant is especially well adapted to 

 living in regions of great exposure to light and heat. 



In Helianthus the flowers are divided distinctly into 

 ray and disk flowers. The ray-flowers are devoid of 

 stamens, and are given over entirely to serve as showy 



