CH. VI, 10] MORPHOLOGY OF FLOWERS 



329 



not are less than the prevalent number, being commonly 

 three in a 5-part flower, or even only one, as prevails through 

 the great Pulse family (Fig. 227). In general a diminution 

 in number accompanies increasing efficiency in function, and 

 marks a higher grade in evolution. Thus the Composite 

 family (that of the Sunflower and Chrysanthemum), the 

 largest plant family, and the one which stands highest of 

 all in plant evolution, has five sepals (when any), five petals, 

 five stamens, and 

 one carpel. 



As the floral leaves, 

 especially the sepals 

 and petals, develop 

 and broaden in the 

 bud, their edges be- 

 come variously dis- 

 posed with respect 

 to one another. In 

 some flowers these 

 parts have their edges 

 exactly matching to- 

 gether without any 

 overlapping, as in the 



FIG. 227. Diagrams of typical flowers, to 

 illustrate deviations from numerical symmetry. 

 Constructed as in Figs. 225, 226. Above, 

 Stellaria and Cassia ; below, a Composite 

 (Helenium) and Primrose. 



Sepals of Fuchsia 



/T ,. oo\ 



(.big. ^Oj, an ar- 



rangement called 



VALVATE. In others 

 the edges regularly overlap spiralwise, as in the petals of 

 Fuchsia, an arrangement called CONVOLUTE. Oftenest they 

 overlap in such manner that some parts have both edges 

 under, some both over, and some both ways, an arrangement 

 called IMBRICATE (Primrose in Fig. 227). These arrange- 

 ments, called collectively AESTIVATION, often persist in the 

 open flowers, though sometimes so lightly as to be easily dis- 

 arranged by a touch or the wind. They are apparently due 

 to a combination of phyllotactic and developmental factors. 



