DICOTYLEDONS : ARCHICHLAMYDEAE 243 



distinguished from them by the hollow or concave recep- 

 tacle, perigynous calyx, corolla, and stamens, and by the 

 fact that these parts of the flower are in whorls and not 

 spirally arranged. The form of the receptacle and the 

 mode of origin and structure of the fruits of this order 

 are interesting ; and the following should be studied as 

 showing transitions from perigynous to epigynous, and 

 apocarpous to syncarpous flowers and fruits. The Meadow- 

 sweet {Spirea Ulmaria) has a nearly flat receptacle ; the fruit 



& 



O 



Fig. 166. 

 1, Floral Diagram of Plum ; 2, Floral Diagram of Apple. 



is a group (aeterio) of two-seeded, twisted follicles. The 

 Tormentil (Potentilla erecta) has a persistent calyx and 

 also an epicalyx ; the receptacle is convex in the middle 

 and bears many dry, one-seeded achenes. The Strawberry 

 (Fragaria vesca) has an epicalyx (Fig. 113, 1), and the central 

 convex part of the receptacle enlarges in the fruit, becomes 

 fleshy, and bears the dry achenes on the outside of it. 

 The Blackberry (Rubus fruticosus) and Raspberry (R. 

 Idaeus) have no epicalyx ; and the column rising from the 

 centre of the flat receptacle bears an aeterio of drupels 



Q 2 



