474 



THE CAMPANULALES 



above the surrounding vegetation. The corolla withers away 

 and the hair-like calyx grows out into a white, delicate pappus, 

 which is lifted upon a beak-like outgrowth of the ovary (Fig. 

 339, F). The fruit is now mature and in a position for distri- 

 bution. The involucre opens, the hairs of the pappus expand, 

 loosening the akenes so that the least touch or breath of air floats 

 off the fruit as a most perfect type of parachute (Fig. 338, c). 



Fig. 340. Inflorescence of the bur-marigold {Bidens), a common ray form 

 of flower of the thistle family: in, involucre. 



{b) The Thistle Family, Carduaceae. — This is the largest 

 family of the angiosperms. The flowers have the same arrange- 

 ment and structure as in the Cichoriaceae, save that the corollas 

 are either all tubular, as in the thistle and ironweed (Fig. 342), 

 or the marginal flowers of the head may be ligulate, thus in- 

 creasing the conspicuousness of the inflorescence, as in the asters, 

 daisy, etc. (Figs. 340, 341). The marginal ligulate flowers are 

 termed ray flowers to distinguish them from the inner tubular or 

 disc flowers. The ray flowers may be sterile, though more fre- 

 quently imperfect and provided with pistils. The calyx may be 

 wanting, but more often assumes the form of silky or plumose 

 pappus or of membranous scales for wind transportation or of 

 barbed bristles of various kinds for distribution by animals. In 

 the case of the burdock {Arctium) the involucre is covered with 



