THE ANGIOSPERMAE 



1101 



An analogous displacement during ontogeny is also probably the origin 

 of the condition in the few observed cases (Dichapetaliim, Lychnis) in which 

 stamens and petals appear to form a single whorl, an occurrence which is 



A 



Fig. 1071. — Floral diagrams. A, Triglochin maritimum. The two whorls of 

 stamens are apparently separated by perianth members. B, Ranunculus 

 acris. Holospiral construction with 13 parastichies. (After Hinner.) 



Otherwise at variance with the theory of zonal differentiation of the floral 

 receptacle, which we shall speak about hereafter (see p. 113 1). 



The arrangement of parts in a flower and its horizontal symmetry can 

 be most simply and clearly expressed in the floral diagram, or ground 

 plan of the flower, on which the various parts are represented as projected in 

 one plane. Developed by Payer and Sachs from the phyllotaxis diagrams of 

 Schimper, the floral diagram showed itself in the hands of Eichler (1875) ^o 

 be an invaluable aid in the analysis of floral structure (Fig. 1072). Sepals 





Fig. 1072. — An illustrative selection of floral diagrams. (Mostly after Eichler.) A, Veronica. 

 B, Lilium. C, Echium. D, Dictamnus. E, Poa. F, Vicia. G, Aconitum. H, Ranunculus. 



