CHAPTER X 



ARRANGEMENT OF THE FLORAL LEAVES 



Like the leaves on the vegetative part of a stem, the floral 

 leaves are arranged in whorls or in spirals. When all its floral 

 leaves are arranged in whorls, a flower is said to be cyclic (e.g. 

 Wallflower, Geranium, Hyacinth) ; but when they are inserted 

 in spirals, the flower is acyclic. Finally, if some of its floral 

 leaves are in spirals and others in whorls, the flower is hemi- 

 cyclic {e.g. most species of Buttercups). 



CYCLIC FLOWERS. 



In the case of a cyclic flower which may be described as 

 a model or a typical flower the following rules hold good : — 

 (i.) The number of floral leaves in each and every whorl of 

 the flower is the same, (ii.) The successive whorls alternate, 

 (iii.) The floral leaves in each whorl are all alike. To take an 

 example : suppose that a flower possesses five sepals, in each 

 other whorl of the flower there should be five floral leaves ; so 

 there might • be five sepals, five petals, ten stamens, and five 

 carpels. The five petals will alternate with the five sepals, and 

 will be succeeded by an alternating whorl of five outer stamens 

 (which are therefore opposite to the sepals) ; the five other 

 stamens will form an inner whorl, and will alternate with the 

 five outer stamens (and therefore be opposite to the petals) ; 

 finally, the five carpels will alternate with the five inner 

 stamens. Comparatively few cyclic flowers conform with all 

 the three rules laid down ; they exhibit variations. 



(i.) Obdiplostemony. — Some flowers have two alternating 

 whorls of stamens, there being in each whorl the same number 

 of stamens as there are petals in a whorl ; but the outer whorl 

 of stamens are opposite to the petals in place of alternating 

 with them. In addition, it is frequently the case that when the 

 number of carpels is the same as that of the petals, the 



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