DESCRIPTIVE TEEMS 



359 



simplest floral types, comparable to the strobilus of some of the 

 lower orders of plants. In the cyclic flowers, like the mandrake 

 and bean, the floral axis, or receptacle, has become greatly short- 

 ened and broadened, so that the floral parts are arranged on the 

 receptacle in cycles instead of spirals as in the marigold. The 

 number of floral parts in each whorl is correspondingly reduced 

 in cyclic flowers on account of the shortening and flattening of 

 the receptacle. With these modifications in the receptacle other 

 changes have 



been gradually /%'\ /?'\ ^Corolla 



introduced with 

 the evolution of 

 flowers, giving 

 rise to what are 

 known as perig- 

 ynous and epig- 

 ynous flowers, 

 as distinguished 

 from the more 

 simply arranged 

 hypogynous flow- 

 ers (Fig. 214). 



Hypogynous flowers have the parts of the perianth and the 

 two sets of essential organs (stamens and pistils) arranged sepa- 

 rately on the receptacle. The spiral flowers of the marigold and 

 the cyclic flowers of the mandrake and bean are common illus- 

 trations of hypogynous flowers with cyclic and spiral arrange- 

 ments of their floral parts. 



Perigynous flowers have a cup-shaped receptacle, which bears 

 the perianth and the stamens on its upper margin. These parts 

 thus appear to surround and inclose the pistil, which remains 

 free in the center of the flower. Flowers of the cherry and of the 

 common wild rose are familiar illustrations of perigynous flowers. 



Epigynous flowers are common in the apple and in many 

 flowers of the Composite?, to which the yarrow and dandelion 

 belong. In such flowers the receptacle is cup-shaped, as in perig- 

 ynous flowers, but yet forms a part of the ovary cavity, which 



> Stamen 

 \- Pistil 



FIG. 215. Complete flower of the alpine azalea 

 (Loiseleuria) 



A, exterior view ; B, sectional view. After H. Miiller 



