DIV. n 



SPERM ATOPHYTA 



551 



assumed on phylogenetic grounds. Thus in the Iridaceae, which are closely 

 related to the Liliaceae, only one whorl of stamens (the outer) is present ; the inner 

 whorl which might have been expected has been lost (Fig. 524). When the 

 position of the missing members is marked by crosses in the empirical diagram the 

 theoretical floral diagram of the Iridaceae is obtained. 



A FLORAL FORMULA gives a short expression for the members of a flower as shown 

 in the floral diagram. Denoting the calyx by K, the corolla by C (if the perianth 

 forms a perigone it is denoted by P), the androecium by A, and the gynaeceum 

 by G, the number of members in each case is placed after the letter. When 

 there is a large number of members in a whorl the symbol oo is used, denoting 

 that the number is large or indefinite. Such a formula may be further made to 

 denote the cohesion of the members of a whorl by enclosing the proper number 

 within brackets ; by placing a horizontal line below or above the number of 

 the carpels the superior or inferior position of the ovary is expressed. 



FIG. 522. Diagram of^ 

 a pentacyclic mono- 

 co\yledonous flower ^-, 

 (Lilium). (After" 

 SCHEXCK.) 



FIG. 523. Diagram of 

 a pentacyclic dico- 

 tyledonous flower 

 (Viscaria). (After 

 EICHLER.) 



FIG. 524. Theoretical dia- 

 gram of the flower of 

 Iris. The missing 

 whorl of stamens is 

 indicated by 

 (After SCHESCK.) 



The floral diagrams in Figs. 522 and 523 would be expressed respectively 

 by the floral formulae, P3 + 3, A3 + 3, G(3) for the Monocotyledon, and K5, C5, 

 A5 + 5, G(5) for the Dicotyledon. __0ther examples are Ranunculus, K5, C5, 

 A oo, G_; Hemlock, Ko, C5, A5, G(2) ; Artemisia, Ko, C(5), A(5), G(2). 



By displacement of the floral members, by inequalities in their 

 size, or by the suppression of some of them, the original radial 

 (actinomorphic) construction (Fig. 525 A] is modified (cf. p. 72); 

 either dorsiventral (zygomorphic) flowers (Fig. 525 B) or completely 

 asymmetrical flowers (Fig. 525 C) may result. In the floral formula 

 indicates an actinomorphic and 4" a zygomorphic flower, e.g. 

 Laburnum, ^ Ko, Co, A (5 + 5), Gl. Zygomorphic flowers always 

 tend to assume a definite position in relation to the vertical. Radial 

 monstrosities of normally dorsiventral flowers are termed peloric. 



2. Ecology. Pollination of Flowers ( 4 ) (cf. p. 201). Many 

 differences in the structure of flowers and in the arrangement of 

 their organs which would otherwise be doubtful are explained when 

 brought into relation to the functions performed by the flower. 

 All flowers have the function of producing progeny sexually ; the 



