370 EVOLUTION OF THE FLOWER 



early in their development to come in contact with one another 

 laterally and to cohere, forming a united structure. This ten- 

 dency is especially noticeable in the megasporophylls, which very 

 frequently cohere into a compound megasporophyll (Fig. 265, 

 C, D), and in the same way the sepals and petals become united, 

 forming a more or less tubular calyx and corolla (Fig. 266, C). 

 The crowding also led to the adhesion of the organs of adjacent 

 sets or whorls. This is ofteij seen in the case of the petals and 

 microsporophylls, the latter organs appearing to arise from the 

 corolla owing to the union of the lower portion of the filament 

 with the base of the petals (Fig. 266, D). 



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 arises 

 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 com- 

 pletely overgrown, so that the other organs of the flower arises 

 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 slight- 

 ly 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 



