CH. XII] DOG-DAISY. 165 



differentiation is carried a step further, the outer florets 

 lose the gynoecium and become sterile or sexless : this is 

 the case with the blue corn-flower (Centaurea). In the 

 dog-daisy the florets have no calyx, but in most plants of 

 the natural order Composite 1 the calyx is present although 

 greatly metamorphosed. In fig. 74, B fine radiating hairs 

 are seen springing from the base of the corolla: these 

 make up what is known as the pappm, which is in reality 

 the metamorphosed calyx. A simpler pappus is seen in 

 fig. 75. 



In figs. 74, 75 it is plain that a structure of some 

 kind projects below the point of origin of the calyx and 

 corolla ; this is the ovary, which in fig. 75 is laid open so 

 as to show the solitary ovule contained within its cavity. 

 It is a striking morphological character of the florets that 

 the ovary is below the point whence spring the calyx and 

 corolla, instead of being, as in the buttercup, above that 

 point. The ovary of the dog-daisy is said to be inferior, 

 that of the buttercup superior : in the following chapter it 

 will be shown that intermediate cases connect these types 

 of floral structure. 



The stamens 2 are five in number and instead of spring- 

 ing from the axis of the flower they arise from the internal 

 surface of the corolla, as may be seen in fig. 74, B and in 

 fig. 75. A similar state of things may be seen in the 

 cowslip flower given in fig. 65, p. 146. The characteristic 



1 The natural order Composite comprises the sunflower, dandelion, 

 groundsel, dog-daisy and many other common flowers. 



2 For the structure and arrangement of the stamens it is well to 

 dissect a floret of one of the garden Centaureas. 



