DEVELOPMENT OF PLANTS 353 



More frequently the receptacle plays an important role in all 

 cases of adhesion. As stated above, its apical portion ceases to 

 elongate at an early period while the basal part continues active, 

 forming a cup about the ovaries. Sometimes the sepals, petals, 

 and even the microsporophylls are so associated with this basal 

 growth of the receptacle that they appear to arise en masse 

 about the ovaries. This growth may be so slight that a care- 

 ful examination of a section of a flower is required to detect 

 it or a conspicuous cup-like structure may be formed, as in the 

 rose (Fig. 266, A, B). This type of flower is termed perigynous, 

 meaning that the receptacle and other organs form a more or 

 less conspicuous cup about the ovaries. In simpler types, as the 

 spiral flowers, it can be seen that the megasporophylls arise at 

 the top of the receptacle and that each of the other organs arise 

 at a point just below the next inner one. Such flowers are called 

 for this reason hypogynous, meaning below the ovaries. Very 

 frequently the basal growth of the receptacle also results in an 

 adhesion to the ovaries which becomes partially or completely 

 overgrown, so that the other organs of the flower arise from 

 the sides or from the top of the ovaries ; the flowers being 

 partially or completely epigynous, meaning that the organs of the 

 flower are developed upon the ovary (Fig. 267, B, D). Often in 

 completely epigynous flowers the receptacle elongates very slightly 

 and the basal portion grows up around the apex forming a 

 cup-like cavity which is roofed over by the megasporophylls. 

 The sporangia or ovules usually arise from the walls of the cavity 

 thus formed and not from the walls of the megasporophylls at 

 the top of the cavity (Fig. 267, D). The calyx, corolla and 

 microsporophylls arise from the top of the structure thus formed 

 and these organs may be developed separately or there may be 

 varying degrees of cohesion and adhesion. 



Another feature to be noted in connection with the evolution 

 of the flower is its symmetry. In the lower types, the organs 

 of a set are alike and radially arranged about the center of the 

 flower ( Fig. 267, A ) . This is the regular or actinomorphic type 

 of flower, meaning radially symmetrical. In many of the orders 

 of angiosperms one or more members of a set are different from 

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