FLOWERS 



105 



95. The arrangement of the organs of the flower. Many of 

 the most familiar flowers have the four sets of organs shown 

 in Figs. 90 and 92. Sometimes there are intermediate forms, 



Fig. 91. Transitions between petals and stamens in the yellow pond lily 



A, external view of flower ; B, a sepal ; C, a petal ; D, E, transitional forms ; 



F, a stamen 



transitional between the parts of one set and those of another, 



— a fact easily understood if all the floral organs represent 

 leaves. The organs are generally arranged in cycles or whorls, 



— that is, in circular fashion around the axis, which is known 

 as the receptacle.^ Often (but not always) the parts of each 



Fig. 92. Flower of stonecrop 



A typical example of the kind of flower in which the members of all four sets of 

 floral organs (sepals, petals, stamens, and carpels) spring separately from a knob- 

 like receptacle. A, entire flower ; B, vertical section. Bothmagnified. After Decalsne 



set stand opposite the spaces between the parts of the adjoin- 

 ing sets; e.g. the petals opposite the spaces between sepals, 

 stamens opposite the spaces between petals, and so on. 



1 In the lowest seed plants, the gymnosperms (pines, spruces, cedars, and 

 so on), the parts of the flower are arranged in a spiral fashion. So, too, are 

 some of the floral organs in the arrowhead {Sagittaria), the pond lily, and 

 the buttercup. 



