386 EVOLUTION OF THE FLOWER 



tendency is especially noticeable in the megasporophylls, which 

 very frequently form a compound megasporophyll (Fig. 265, 

 C, D), and in the same way the sepals and petals may appear as 

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

 crowding also led to the mass growth of the organs of adjacent 

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

 microsporophylls, the latter organs appearing to arise from the 

 corolla (Fig. 266, D}. 



The receptacle plays an important role in all cases of mass 

 growth. 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. The sepals, petals, and even the micro- 

 sporophylls are often so associated with this basal growth of 

 the receptacle that they arise en masse about the ovaries. This 

 growth may be so slight that a careful examination of a section 

 of a flower is required to detect it or a conspicuous cup-like struc- 

 ture 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 hypo- 

 gynous, meaning below the ovaries. 



Very frequently the basal growth of the receptacle also involves 

 the ovaries which becomes distinct from the mass growth at 

 various stages in their development. Consequently the other 

 organs of the flower appear to 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 



