CHAP. iv.J REPRODUCTION OF PLANTS. 151 



The maximum of development in the massing together 

 of minute flowers to form an effective mass has been 

 attained by the various members constituting the order 

 of plants known as Gompositw, represented by such well- 

 known plants as thistles, dandelions, daisies, chrysan- 

 themums, sunflowers, etc., where the head in all cases does 

 not consist of a single large flower, but of an enormous 

 assemblage of closely-packed small flowers. In addition 

 to the idea of concentration of small flowers met with in 

 Compositse, we are also introduced to a high development 

 of division of labour in many instances. In the common 

 dog-daisy {Bellis perennis) the central yellow portion of 

 each head of flowers consists of minute yellow florets ; 

 these collectively form the disc, their function being 

 more especially to produce seeds, whereas the white 

 radiating portion of the head, each portion of which re- 

 presents a flower, serves for attractive purposes, the 

 florets being incomplete and not producing seed. Both 

 disc and ray florets have the petals adhering together, 

 but in the former the corolla is regular, in the latter 

 irregular. A similar division of labour is seen in the 

 inflorescence of the ox-eye daisy {Chrysanthemum leu- 

 canthemum), sunflower {Helianthus awwMMs), etc., whereas 

 in the dandelion {Taraxacum officinale), and the thistles 

 {Oarduus), all the florets are fertile and of one shape, 

 showing no division of labour in the direction indicated 

 above. 



In the case of scattered flowers, each flower originates 

 in the angle between a, floral-bract or leaf-like structure, 

 and the stem, each flower with its floral-bract being 

 separated from those above and below by a naked portion 

 of flower-stalk ; in such cases the flowers are protected 



