HELIANTHUS ANNUUS. 171 



organs for the entire group, no seeds even being ripened 

 within the ovaries of these flowers. The seeds are formed 

 in the disk-flowers, one seed forming in each ovary. These 

 conditions do not obtain for all Composite, however. In 

 some, such as the dandelion (Taraxacum), all the flowers 

 are like ray-flowers; while in some others, such as the yar- 

 row (Achillea millejolium) , all are tubular disk-flowers. In 

 some, such as the rosinweed (Silphium) the ray-flowers 

 mature seeds, although they have no stamens. 



The Composite are remarkably successful as a group, 

 being abundantly distributed almost everywhere during 

 summer and autumn. They probably constitute the 

 youngest and most successful group of plants. 



