354 THE FLOWER 



the cup-shaped receptacle may be fused with the walls 

 of the carpels (Fig. 60, D: apple, pear). These 

 different relations of the receptacle to the various whorls 

 of the flower are expressed by the terms hypogynous, 

 perigynous and epigynous,^ the other whorls of the 

 flower being below the gynsecium in the first case, 

 round it (i.e. borne on the edges of the receptacular cup) 

 in the second, and above or on it in the third, where 

 the sides of the receptacle are fused with and close over 

 the walls of the carpels. 



On the whole, in the evolution of the great group 

 of flowering plants, the flowers with separate and numer- 

 ous floral leaves are more primitive, those with few and 

 joined floral leaves the more advanced (the stamens, 

 having thin stalks, generally remain separate throughout, 

 though they are joined to one another in a few cases). 

 And the perigynous and epigyhous types of flower 

 are similarly more advanced than the hypogjoious. 

 Especially in the case of the carpels, as we pass from more 

 primitive to more advanced flowers, there is a tendency 

 for the carpels {a) to decrease in number, (6) to become 

 fused, and (c) to become enclosed in the receptacle. 

 The ovary is said to be inferior in this last (epigynous) 

 type of flower (apple, narcissus). 



Besides these general tendencies in the evolution of 

 flowers there are many other differences depending 

 on the relative size, shape and colour of the different 

 floral leaves. These affect particularly the mode of 

 pollination. A flower has to be regarded as a whole, 

 as an organ which not only produces and protects 

 the spores and gametes but is also so constructed as 

 to bring about the conjugation of the gametes through 

 the preU'minary process of pollination. In many cases 

 ' Greek vtt6, irepi and iirt, below, round and on. 



