FLOKAL SYMMETRY. 175 



equal number of parts in a cycle, and the cycles alternating 

 with each other, is simply that of verticillate phyllotaxy. (234.) 

 In either case, the members of the successive circles (or of 

 closed spirals as the case may be) will be equal in number ; that 

 is, the flower will be isomerous. 



317. A Symmetrical Flower is one in which the members of all 

 the cycles (whorls or seeming whorls) are of the same number. 1 

 In nature, the symmetry is of all degrees : it is most commonly 

 complete and perfect as to the floral envelopes when it is not 

 so as respects the essential organs. The general rule is that 

 the successive cycles alternate, as is the nature of true whorls. 

 But the superposition of successive parts is not incompatible 

 with symmetry of the blossom, although it is a departure from 

 the ordinary condition, assumed by botanists as the type. An 

 isomerous flower (meaning one with an equal number of mem- 

 bers of all organs) is the same as symmetrical, if the reference be 

 to the number in the circles, rather than to the total number of 

 organs of each kind. % 



318. A Regular Flower is one which is symmetrical in respect 

 to the form of the members of each circle, whatever be their 

 number ; i. e. , with the members of each circle all alike in shape. 



319. These two kinds of symmetry or regularity, with their 

 opposites or departures from symmetry, need to be practically 

 distinguished in succinct language. For the terminology, it is 

 best to retain the earlier use, generally well established in phyto- 

 graphy, as above defined. 



320. A Complete Flower is one which comprises all four or- 

 gans, viz. calyx, corolla, stamens, pistil. 



1 This is not only the definition " generally applied in English text-books," 

 but that introduced by DeCandolle, adopted by St. Hilaire, and followed at 

 least by the French botanists generally. The innovating German definition, 

 of a recent date, is that a symmetrical flower is one " that can be vertically 

 divided into two halves each of which is an exact reflex image of the other." 

 But such have immediately to be distinguished into " flowers which can be 

 divided in this manner by only one plane," which Sachs terms " simply 

 symmetrical or monosymmetrical," and those which can be symmetrically 

 divided by two or more planes, " doubly symmetrical or poll/symmetrical," 

 as the case may be. Now both these forms have a more expressive and 

 older terminology, adopted by Eichler, viz. : 



Zygomorphous, for flowers, or other structures, which can be bisected in 

 one plane, and only one, into similar halves (median zygomorphous, when 

 this is a median or antero-posterior plane, as it most commonly is ; tram- 

 verse zygomorphous, when the plane of section is transverse or at right 

 angles to the median, as in Dicentra) ; 



Actinomorphous for flowers, &c., which can be bisected in two or more 

 planes into similar halves. 



