CHAPTER XXXIII. 



OOMPOSITiE. 



I. The Coinpositse is the most extensive Order, and comprises 

 from 10,000 to 12,000 species, or roughly about one-tenth of all 

 known seed-bearing plants. 



A number of species, such as Arnica montana L., chamomile 

 and wormwood, are of medicinal value ; others, of which the 

 artichoke and lettuce may be taken as examples, are useful food 

 plants of the garden. 



Plants belonging to the genera Zinnia, Chrysanthemum, 

 Dahlia, Aster, Gaillardia, Helianthus, and others are largely 

 grown as ornamental plants. 



Not a single species, however, is grown as an ordinary farm 

 crop in this country, though not a few, such as dandelion, thistle, 

 groundsel, coltsfoot, mayweed, and ox-eye daisy are objectionable 

 weeds (see pp. 592, 605^. 



2. General characters of the Order. — The most characteristic 

 feature of the Order is the structure of the inflorescence : the 

 latter is a capitulum, and consists of a number of small flowers 

 collected into a compact head resembling a single large flower. 



A common form of capitulum is seen in the ox-eye daisy 

 (Fig. 147), the parts of which, with the dandelion described below, 

 may be taken as typical of the commonest forms in the Com- 

 positae. On its underside is a series of narrow scaly bracts 

 termed phyllaries, arranged in whorls; the whole series of 

 phyllaries is spoken of as the involucre of the capitulum. 



In the centre of the capitulum are a number of small yellow 

 flowers — the so-called disk florets — each of which has the 



