368 THE FRUIT 



frequently sterile, with a conspicuous one-sided corolla, 

 so that the whole flower-head looks like a single flower 

 (daisy). Here the gynaecium of each flower consists 

 of two united carpels, the ovary being inferior. Only 

 one carpel, however, with one seed, comes to maturity. 

 The wall of the ovary really consists of receptacle 

 and pericarp fused, but since it is membranous and 

 one-seeded the mature fruit is for practical purposes 

 an achene, though it is derived from a bicarpellary inferior 

 ovary. 



A nut is a one-seeded fruit with a woody pericarp. 

 Here again it may be derived from a bicarpellary inferior 

 ovary, as in the common hazel nut (Corylus). 



Dry fruits which contain many seeds are practically 

 always dehiscent, i.e. they open to let out the ripe seeds. 

 A simple example is a pea or bean pod. This consists 

 of a single elongated carpel held horizontally in the 

 flower, and generally more or less flattened laterally. 

 The lower edge is the midrib of the carpellary leaf, 

 the upper edge the joined margins (placentae) bearing 

 the seeds. The seeds and the ovary grow very con- 

 siderably before ripening, multiplying their original 

 size many times over. When fully grown the walls 

 dry and split along both edges, the seeds being easily 

 detached and falling to the ground. Practically all 

 the pea family (Papilionaceae) have this type of fruit 

 (legume). The marsh marigold, hellebore, columbine, 

 larkspur and monkshood all members of the butter- 

 cup family (Ranunculaceae) have similar fruits, but 

 they have several separate carpels in each flower, and 

 the fruit splits along the placental margin only (follicle). 



Many dry dehiscent fruits are formed from syncarpous 

 gynaecia, with axile, free central or parietal placentation 

 Fig. 6 1 (foxglove, corncockle, violet). These all open by 



