THE FLOWER to^ 



IsoMERiTY OF Flowers. — When the calyx, corolla, 

 andrcecium, and gyncecium of a flower consist of the 

 same number of segments, or some multiple of that 

 number, the flower is said to be isomerous. Other- 

 wise it is ANisoMEROUS. An isomerous flower may 



be DIMEROUS, TRIMEROUS, TETRAMEROUS, Or PENTA- 



MEROUS, according as the number of segments in 

 each whorl is 2, 3, 4, or 5, or some multiple of them. 

 Common instances of an isomerous flower are pathar- 

 kucha (Bryophyllum calycinum) and him-sagar (Kal- 

 anchoe) (see fig. 183), in both of which there is one 

 whorl of calyx with four sepals, one whorl of corolla 

 with four petals, two whorls of andrcecium with four 

 stamens in each whorl, and one whorl of pistil with 

 four free carpels. Such all-round isomerity is rare 

 amongst Dicotyledons. Usually the number of seg- 

 ments in all whorls, excepting the pistil, is taken into 

 account in determining the isomerity of a flower, as 

 the number of segments of the pistil is, as a rule, less 

 than the number of segments of the other whorls. 



Symmetry of Flowers.— A flower is said to be 

 SYMMETRICAL when it can be divided by one or more 

 vertical planes, passing through its centre, into two 

 equal and similar halves, while a flower which cannot 

 be so divided is said to be asymmetrical. Sym- 

 metrical flowers are monosymmetrical or zygomor- 

 PHic when they can be divided into two equal and 

 similar halves by one such vertical plane only, as in 

 Pea; and polysymmetrical or actinomorphic when 

 they can be so divided by two or more such vertical 

 planes, as in rajani-gandha or Tuberose. 



Floral Diagrams. — The number, arrangement, 

 and nature of the whorls of a flower and of their seg- 

 ments is often represented by a diagram known as 

 floral diagram. In a floral diagram the successive 



