262 SYSTEMATIC BOTANY 



The characteristic feature of the order is the highly 

 specialized inflorescence ; many small flowers being con- 

 densed into a conspicuous head or capitulum. Division of 

 labour is so well developed that a capitulum resembles 

 a single flower (see p. 155, Fig. 104), and the arrangements 

 for pollination by insects and dispersal of the pappose fruits 

 by the wind, are so perfect that the flowers represent the 

 highest stage of development yet reached by flowering plants. 



The order is divided into two main groups : 



(1) Tubuliflorae. Plants without milky latex and the 

 florets of the disk tubular, not strap-shaped, e. g. Daisy, 

 Coltsfoot (see pp. 178-80, Figs. 122 and 123), and 

 Thistle. 



(2) Liguliflorae. Plants with a milky latex and the 

 florets all strap-shaped, e. g. Dandelion (see p. 181, 

 Fig. 124), Goat's-beard, and Hawkweed. 



Interesting modifications are met with in the florets of the 

 same capitulum as regards distribution of stamens and 

 pistils, and the following should be studied : 



Usually the ray florets are female and the disk-florets 

 hermaphrodite as in the Daisy (Bellis perennis) (see p. 178), 

 Dog Daisy (Chrysanthemum Leucanthemum) , and Corn 

 Marigold (C. segetum). In the Sunflower (Helianthus 

 annuus) the ray-florets are ligulate and neuter ; the 

 disk-florets tubular and hermaphrodite. The Cornflower 

 (Centaurea Cyanus) has tubular and neuter ray-florets and 

 tubular and hermaphrodite disk-florets. The Butter-bur 

 (Petasites vulgaris) is dioecious ; the male heads are few- 

 flowered (about thirty), produce honey and pollen, and 

 have a barren ovary and style. The female heads are larger 

 (about 150 florets) ; two or three of the outer ones are 

 male, the rest being female and producing no honey 

 or pollen. The Groundsel (Senecio vulgaris) has no ray- 

 florets, is inconspicuous and self-pollinated. The Ragwort 



