502 PART III. THE CLASSIFICATION OF PLANTS. 



ferae ; perianth of Urtica and Moras). Where the whorls are 

 trimerous the dicjclic condition is frequent : thus in the majority 

 of Monocotyledons there are two whorls of stamens whilst all the 

 other series of the flower are monocyclic, so that the flower is 

 diplostemonous with regular alternation : in the comparatively 

 few trimerous flowers of Dicotyledons the dicyclic condition may 

 be observed in the androecium (Rheum, Polygonum, Berberis), or 

 in -calyx, corolla, and androecium (Cocculus). The f calyx, which 

 is to be found in very many Dicotyledons, may be regarded as 

 equivalent to a dicyclic calyx (see p. 497). A dicyclic gynasceum 

 is to be found in a few Monocotyledons (e.g. Alisma, Butomus) 

 and Dicotyledons (Phytolacca, and Malvacese such as Malva, 

 Althaea, Lavatera). 



The conclusion to be drawn from these facts is that in the com- 

 plete dichlamydeous ambisporangiate flowers of Angiosperms there 

 are, as a general rule, five whorls of floral leaves ; the flowers are 

 pentacyclic. In most Monocotyledons the five whorls belong, one 

 to the calyx, one to the corolla, two to the androecium, and one to 

 the gynaeceum: in most Dicotyledons they belong, two to the calyx, 

 one to the corolla, one to the androecium, and one to the gynaeceum. 



If, now, such a pentacyclic flower with regularly alternating 

 whorls be taken as a type or standard of comparison, it will be 

 observed that many flowers deviate from it by having either a 

 larger or a smaller number of whorls, the deviation being combined 

 in some cases with direct superposition. 



Pleiotaxy, or an increase in the number of the whorls in a flower, 

 is characteristic of a number of genera belonging to various 

 natural orders. Instances have been mentioned above of Mono- 

 cotyledons and of Dicotyledons having flowers with a dicyclic 

 gynaeceum ; of Dicotyledons with a dicyclic corolla or androe- 

 cium : but the number of whorls is sometimes much greater 

 (15- in Aquilegia), when the flowei'S, as also the special series, are 

 said to be polycyclic. Thus, the calyx is polycyclic in Nandina 

 (Berberidaceae) and in Sychnosepalum (Menispermaceae) ; the 

 androecium, in Aquilegia, Camellia, Rosa, Lauraceoe, and Papaver- 

 aceae ; the gynaeceum, in some Alismaceae and Butomaceae. In 

 some cases, one series becomes polycyclic at the expense of 

 another : thus in the acyclic flowers of Clematis, Anemone, and 

 Caltha, the petals are replaced by stamens so that the number of 

 turns of the spiral ( = whorls) in the androecium is increased whilst 

 the corolla disappears. The " doubling " of flowers is commonly 



