DEVELOPMENT OF PLANTS 



415 



monly in five's and cyclic (Fig. 310, A) though the spiral ar- 

 rangement still persists in nearly every family of the order. The 

 most distinguishing feature of the group is seen in the adhesion 

 of the receptacle to the calyx, thus lifting up the corolla and 

 stamens about the ovary (perigynous flowers) and this growth 

 also frequently results in an adhesion to the ovary (epigynous 

 flowers). The simple forms of flowers that appear in many of 

 the families are very suggestive of the Ranales, the sporophylls 

 being free and often spirally arranged. Thus, in the live-for- 



Fig. 310. Simple forms of the Rosales : A, flower of Sedum, showing 

 the radial symmetry of the flower and five organs in each whorl. B, grass 

 of Parnassus (Pamassia), a member of a closely-allied family. C, flower 

 on first day of bloom, stamens converging over the pistil and encircled by 

 row of modified stamens. D, section of flower, showing slight growth of 

 base of receptacle and consequent adhesion to perianth. This flower is 

 protandrous and the stamens in shedding the spores straighten up one by 

 one on succeeding days and curve back towards the petals. The section 

 shows three positions assumed by the stamens. You may calculate the 

 significance of these features. 



