THE HIGHER DICOTYLEDONS. 



377 



flower, into a strap with five teeth at the end ; this is the true 

 ligulate type. In most heads of the Daisy type the strap- 

 like lower lip of the ray-flowers is either entire or divided 

 into three lobes at the end. Other "falsely ligulate" types 

 are seen in the numerous " double " varieties of Dahlia, etc. 



The Composites are practically all insect-pollinated, and 

 have a beautiful and effective mechanism of a comparatively 

 simple type, already described for Dandelion (Art. 369). 

 The grouping of the small flowers into heads an arrange- 

 ment not peculiar to Composites but found in many other 



"STIGMA 



ANTHERS 



'COROLLA 



COROLLA 



.CALYX 

 -'OVARY 



NEUTER FLOWER {* FLOWER 



Fig. 154. Cornflower (Centaurea). 

 I., Outer neuter flower ( X 3) ; II., Tubular hermaphrodite flower ( X 6), 



families, e.g. Scabious, Sheep's-bit, Sea-Holly, Clovers- 

 brings about a saving in corolla-material, besides enabling a 

 single insect-visitor to pollinate several flowers in a short 

 time and causing the flowers to form a conspicuous mass 

 (this is heightened by the frequent arrangement of the heads, 

 when small, in corymbs or racemes, or even in Globe Thistle 

 compound heads, i.e. heads of heads). 



Most species of Centaurea (Fig. 154) have irritable stamens, 

 sensitive to contact. When an insect touches the stamens, the 

 filaments contract and force a mass of pollen out from the top 

 of the anther-tube. The mechanism is easily observed in the 

 Cornflower. With a camel-hair brush or a pointed match- 

 stick remove the pollen projecting from the anther-tube of a 



