io6 THE BOOK OF NATURE STUDY 



unequal growth of the floral receptacle. The receptacle in 

 the Buttercup is conical, and the sepals, petals, stamens, and 

 carpels stand in the order named from below upwards upon it 

 (Fig. 53, B). The relation of the various parts is that shown 

 in the diagram (Fig. 58, A). In many flowers, however, the region 

 of the receptacle that bears the sepals, petals, and stamens grows 

 more actively, and widens out into a plate-like (Fig. 58, B) or cup-like 

 (Fig. 58, B') structure bearing these parts on its edge around the 

 pistil, which remains on the true summit of the receptacle. A 

 still further modification is reached when the hollow receptacle is 

 joined to the wall of the ovary (Fig. 58, c). The sepals, petals, and 

 stamens now appear to spring from the upper surface of the 

 ovary, while the styles stand up in the centre of the flower. In 



A B 3' 



FIG. 58. Forms of receptacle of the flower. (From Strasburger's 

 Lehrbuch der Botantk.} 



this case the ovary is spoken of as inferior, while in the two former 

 cases (A and B) it is termed superior. 



Flowers also differ in their general symmetry. In the Buttercup 

 and many other flowers the floral leaves are disposed symmetrically 

 around the centre of the flower, which could be divided into equal 

 and similar halves by a number of planes passing through the 

 centre. Such flowers are called regular. In many other flowers, 

 however, we can recognise an upper and lower side, and right 

 and left halves. The parts are no longer placed symmetrically 

 around the centre, but differences in either their number or in their 

 size and shape lead to the flower being symmetrical with respect 

 to one plane of division only. Such flowers are termed irregular, 

 and many of the flowers most highly specialised in relation to 

 their insect visitors will be found to be of this kind. The Violet, 

 the Dead-Nettie, and the Orchid are good examples from among 



