AGGREGATE. 



565 



these may be one scale (bract) for each flower (Fig. 610 lr), or a 

 large number of bristles, which do not each correspond to a leaf, or 

 the receptacle may be entii-ely without covering (naked). The flowers 

 open in acropetal order in each capitulum. All the flowers in a 

 capitulum may be of the same sex, and their form and colour are in 

 that case the same, or the sexes may be different, in which case the 

 form and colour are also most frequently different : the ray-flowers 

 have projecting labiate or ligulate corollas, while the disc-flowers 

 have tubular corollas. As a rule in the latter case the ? -flowers 



FIG. 605. Calendula arvensis: A capitulum; B capitulum in longitudinal section; 

 C ? -flower ; D $ -flower ; E the stamens ; F capitulum with ripe fruits; Gf ripe fruit. 



are at the circumference, and the ^ in the centre, less frequently 

 ? -flowers at the edge and ^-flowers in the centre. The ray- 

 flowers in some genera are neuter (e.g. Centaurea). Some are 

 dioecious. 



There is no trace of an epicalyx (in contrast to the Dipsacaceae, 

 which they generally so resemble). The formation of the CALYX 

 is very varied. The calyx always consists of a very small 

 cushion-like structure, most frequently developed later than the 

 corolla ; the 5 corners, which correspond to the 5 sepals, in a few 



