THE FLOWER. 91 



trimerous or ternary (fig. 161), tetramerous or quaternary, and pen- 

 tamerous or quinary (fig. 162). The ternary arrangement is by far 

 the most common in the Monocotyledons, the quinary in the Dico- 

 tyledons. 



Most frequently the calyx and corolla have Fig. 162. 



an equal number of parts; the relative num- 

 ber of organs is prone to increase in the stami- 

 nal circles, and still more frequently to dimin- 

 ish in the carpellary whorl. 



Alternation or Superposition. In the 

 majority of cases we find the organs of 

 each successive whorl developed alternately 

 with, and not super- or anteposed to, those 

 of the preceding circle. 



From this the whorls would appear to re- 

 semble the decussating whorls of true leaves, 

 rather than regularly succeeding spiral cycles. 

 We have seen that these decussating whorls are closely related to the 

 spiral cycles (p. 48). Moreover we find in the very numerous cases of 

 flowers with the organs imbricated in the bud, that the spiral arrangement 

 is very evident, and the whorled appearance presents itself only after the 

 expansion of the flower. Now, if the or f cycles succeeded regularly, 

 the organs of successive cycles should be superposed and not alternate, as 

 indeed they sometimes are, e. g. Sabia. A. de Jussieu has supposed that 

 the organs are arranged on the spiral T 5 type in all trimerous and penta- 

 merous flowers with imbricated aestivation. Inspection of the diagrams 

 in a former page (45) will show with how little displacement the organs 

 of such flowers may be arranged on this type ; and there is much proba- 

 bilitv that the alternation of spirally arranged cycles results from some 

 such" cause, while the alternation of organs in flowers with valvate aesti- 

 vation is referable to the same laws as the decussation of whorls of leaves. 

 The exceptional case of opposition of organs will be explained presently. 



Typical Flower. The typical flower in the diagrams (figs. 157, 

 162) consists of four circles of organs equal in size and number of 

 parts, and with the parts regularly alternating. A flower thus pre- 

 senting all the whorls is called complete or eucyclic ; the organs 

 in each circle being similar, it is regular and the number of organs 

 in each circle being the same, it is moreover isomerous. 



Modifications. Almost every kind of deviation and combination 

 of deviations from this type are met with ; but the modifications 

 in the number, arrangement, and form of whorls or parts are refer- 

 able to distinct causes, such as: 1. Alteration of the number of 

 circles, or of the number of organs in the circles ; this may arise 

 either from multiplication, ctiorisis, enation, or interposition, or from 

 suppression or abortion of parts. 2. Union of the organs ; this 



