384 



EVOLUTION OF THE FLOWER 



consists of a few scales as in the sweet flag, oak, etc. (Fig. 263, B), 

 but in higher forms, the perianth appears as the conspicuous 

 leafy portion of the flower as in the lily (Fig. 263, C). Finally 

 flowers appear in which the leaves of the perianth become dif- 

 ferentiated into an outer calyx composed of several green sepals 

 and a corolla of larger, more delicate and often brightly-colored 

 leaves, called the petals (Fig. 263, D). We have now reached a 

 point where the flower is said to be complete, consisting of all 

 the organs that are normally associated in the flower. 



Fig. 264. Fig. 265. 



Fig. 264. Flower of strawberry with elongated receptacle bearing nu- 

 merous spirally arranged sporophylls: A, open flower. B, flower in section, 

 showing arrangement of parts upon receptacle, r, which forms a shallow cup 

 at base bearing the perianth and microsporophylls. C, the fruit or enlarged 

 receptacle bearing the minute spirally-arranged megasporophylls. 



Fig. 265. Flowers with shortened receptacles: A, flower of Pyrola with 

 calyx and corolla arranged in whorls or cycles. B, section of flower, showing 

 all the organs in cycles." C, flower of geranium. D, flower with corolla 

 removed to show the coherence of the five megasporophylls that results from 

 the shortening of the receptacle. 



As stated above the simpler type of flower is characterized 

 by numerous sporophylls, spirally arranged and separately at- 

 tached to an elongated receptacle. One of the most important 

 variations that appeared in the evolution of the flower is asso- 

 ciated with the shortening of this receptacle. This is brought 



