COMPOSITAE COMPOSITE FAMILY 



This is the largest family of flowering plants, likewise the 

 highest as it ranks above all others in complexity of structure 

 and physiological processes, in relationship to insects and in 

 method of seed dispersal. Some of its members are pernicious 

 weeds, many are used as garden and greenhouse flowers, but 

 otherwise surprisingly few are of economic importance. 



The individual flowers in this family are small and pro- 

 duced in dense clusters called heads. What is commonly 

 called a Dandelion flower, for example, is really a head com- 

 posed of a large number of individual flowers. In the case of 

 the Dandelion all the flowers have flat straphke corollas. In a 

 plant like the Sunflower, on the other hand, the outermost 

 flowers of the head, called ray flowers or more commonly rays, 

 have strap-shaped corollas; the others, in the center and called 

 disk flowers, have tubular corollas. A third type of head, such 

 as in the White Snakeroot, has the corollas of all its flowers 

 tubular. 



The calyx, always above the ovary, is very much modified 

 in these flowers and is called a pappus. In some cases it is 

 composed of hairlike bristles and in others of awns or scales, 

 and in a few genera it is lacking. The style of the sterile 

 flower is always 2-cleft, 



The head is in all cases surrounded by an involucre of more 

 or less leafhke bracts. In many species there are bracts or 

 scales on the receptacle among the flowers, spoken of as 

 chaff. When they are absent the receptacle is said to be naked. 



Cross-pollination is the rule among the Composites. In all 

 species described in this book the anthers are grown together 

 around the style and the pollen sacs open on the inward side. 

 As the flower opens, the style, with its stigmas closed, pushes 

 up through the united anthers, scraping pollen from them. 

 The pollen mass remains partly adherent to the anthers and 

 falls over onto their upper ends, instead of being carried along, 

 as the style grows past. Only after the style has grown beyond 

 the anthers do the stigmas open to receive the pollen which 

 insects will bring from other flowers. 



It will often require close observation to distinguish the 

 different kinds of Composites but there should not be much 

 difficulty in recognizing the ones included in this book. Many 

 not included here are likely to be found, however, and for them 

 more comprehensive manuals should be used. 



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