FLOWERS, THEIR STRUCTURE AND KINDS 153 



The Sunflower. 

 (Helianthus annuus.} 



252. The sunflower is widely cultivated in gardens for its 

 showy flower head, and for the seed, which is considered a 

 healthful food to be given occasionally to poultry and stock. 

 It grows wild along the rich river valleys in some of the Western 

 States. 



The sunflower is an excellent example for the study of the 

 type of flowers which form a head. The " flower head" is made 

 up of a large number of flowers crowded very closely together in 

 a rounded or flattened group on the broad receptacle.* Each 

 one of these flowers is called & floret. In the sunflower head there 

 are two kinds of flowers. The most showy flowers in the head 

 are the long yellow strap-shaped ones on the border of the head, 

 where they extend outward in the form of rays. These are 

 called ray flowers. The disk flowers are very great in number 

 and occupy the space inside of the circle of ray flowers. The 

 corolla is tubular in form, and the disk flowers are often called 

 tubular flowers. Each disk flower grows by the side of (really 

 in the axil of) a slender pointed bract. On the outside of the 

 head are a large number of overlapping green leaf -like members, 

 each with a long, narrow, pointed end. These are bracts which 

 together make up the involucre, which encloses the head in the 

 young stage. 



253. The disk flowers or tubular flowers. The flowers 

 should be studied in the different stages of flowering. The mode 

 of inflorescence is centripetal. The flowers on the outer margin 

 of the disk open first, while those in the center are still quite 

 young. These form a circle, and as they pass the height of the 

 flowering period another broad circle of flowers just inside the 

 outer ring come into the height of flowering. The circle of 



* Such flowers are often called compound flowers. The family to which 

 the sunflower belongs is the Composite, and its members are often spoken 

 of as composites. Besides the sunflower it includes such plants as the golden- 

 rod, aster, daisy, yellow-eyed-susan, dandelion, chicory, lettuce, Joe-pye- 

 weed, chrysanthemums. 



