THE FLOWER ITS PARTS AND FORMS 



141 



FIG. 189. HEAD OF SUNFLOWER. 



florets are inclosed in a more or less dense and usually 

 green involucre. In the thistle (Fig. 190) this involucre is 

 prickly. A longitudinal 

 section discloses the flo- 

 rets, all attached at bot- 

 tom to a common torus, 

 and densely packed in 

 the involucre. The pink 

 tips of these florets con- 

 stitute the showy part of 

 the head. 



Each floret of the this- 

 tle (Fig. 190) is a com- 

 plete flower. At a is the ovary. At b is a much-divided 

 plumy calyx, known as the pappus. The corolla is long- 

 tubed, rising above the pappus, and is enlarged and 5-lobed 



at the top, c. The style pro- 

 jects at e. The five anthers 

 are united about the style in 

 a ring at d. Such anthers 

 are said to be syngenesious. 

 These are the various parts 

 of. the florets of the Com- 

 positae. In some cases the 

 pappus is in the form of 

 barbs, bristles, or scales, and 

 sometimes it is wSnting. 

 The pappus, as we shall see 

 later, assists in distributing 

 the seed. Often the florets 

 are not all alike. The corolla 

 of those in the outer circles may be developed into a long, 

 straplike, or tubular part, and the head then has the ap- 



FIG. 190. LONGITUDINAL SECTION 

 OF THISTLE HEAD; also a FLORET 

 OF THISTLE. 



