216 PLANT-LIFE 



Of all the vegetable kingdom, according to our present 

 knowledge, and if our interpretation of the facts is cor- 

 rect, the Aggregatce are the most specialized and the 

 highest. These are anisocarpous plants, with flowers 

 aggregated into heads, each fiowerhead being surrounded 

 by an involucre of bracts. The stamens are placed on 

 the petals, and the ovary is inferior (p. 213). The less 

 specialized of this highly developed group are the Honey- 

 suckles, the Teazels, and various species of Scabious. 

 The highest development is observed in the Compositse, 

 including about 10,000 species. Here we have the 

 Daisies, Sunflowers, Asters, Chrysanthemums, Dande- 

 lions, Hawkweeds, etc., which are frequently, but rather 

 loosely, referred to as " compound " flowers. In some 

 forms — for example, the Daisy [Bellis perennis) — there 

 are two kinds of florets — the " disc " and the " ray." 

 The latter make the flowerhead conspicuous ; in some 

 cases they are sterile. The flowerhead of the common 

 Daisy, although it is commonly spoken of as " a flower," 

 is composed of about 250 individual flowers compacted 

 together. Of these, about fifty are white, straplike 

 "ray" florets, each having a pistil, but no stamens; 

 while about 200 tubular, five-cleft yellow flowers, with 

 stamens and pistil, form the central disc. The lobes of 

 the corolla of the yellow disc-florets indicate that five 

 petals have cohered to form this floral envelope, and 

 doubtless the same number of petals have entered in 

 combination to form the straplike corolla of each ray 

 floret, although here sympetaly is so far advanced that 

 there is little sign of the primitive five petals. Yet care- 

 ful examination of the base of one of these white florets 

 yields the impression of the floret being a split tube. 



