12 
PHANEROGAMS. 
while in hemicyclic flowers those members at least which are arranged in whorls may 
possibly be distributed symmetrically. If, on the contrary, the parts are all arranged in 
whorls, they are usually distributed monosymmetrically or polysymmetrically on the 
receptacle. Thus, for example, the diagram Fig. 406 can be divided symmetri- 
cally and regularly by three planes. Fig. 407 by four, and Fig. 408 by five planes. 
The diagrams Fig. 409 B and C, as well as Fig. 410, can, on the contrary, be symmetri- 
cally halved by only one plane, which is at the same time the median plane. The diagram 
Fig. 411 can be divided by the median plane into two symmetrical halves which are 
unlike those produced by the lateral section ; this diagram is, like those in Figs. 409 B, C 
and 410, zygomorphic, but is doubly while these are only singly symmetrical \ 
The symmetry of mature unfolded flowers is indeed usually connected genetically 
with the relations of symmetry of the diagram (which represents only the position and 
number of the parts) ; as will be made clear by a comparison of Figs. 416 and 418 with 
Fig. 410 y^. But inasmuch as the entire form of the mature flower is essentially deter- 
FlG. 417.— Zyg-omorphic flower of Poly^ala sra7idiflora: A entire flower seen from the side after removal of one 
sepal k ; B flower divided symmetrically without the gynfficeum ; C the gynaeceum magnified ; D horizontal section 
of the ovary ; E median longitudinal section of the ovary ; F horizontal section of the flower ; k calyx, c corolla, 
st staminal tube, cp gynophore, / ovary, g style, n stigma, sk ovules, xx the tube formed by the adhesion of the 
petals and stamens. 
mined by the shape, size, torsion, and curvature of the separate parts, these circum- 
stances also exert a preponderating influence on the relations of symmetry of the open 
flower, and to such a degree that even flowers which have their parts arranged spirally 
may become monosymmetrically zygomorphic in reference to their entire form, as is 
the case to a high degree, for example, in Aconitum and Delphinium. It must however 
be observed that the zygomorphism of the flower is here brought about principally or 
entirely by the calyx and corolla, the spiral arrangement of which may perhaps still be 
doubtful, but which always occupy so narrow a zone on the receptacle that their position 
may be considered practically to be verticillate. If, on the other hand, the floral axis is 
sufficiently elongated to show that the arrangement is a distinctly ascending spiral one, 
as in the perianth and androecium of Nymphcea and the androecium and gynaeceum of 
Magnolia, the subsequent development of the organs appears also not to show any zygo- 
morphic nor indeed generally any kind of actually symmetrical arrangement. 
* The beginner may make these relations more evident to himself by placing a small mirror with 
smooth edge vertically upon the paper so as to bisect the diagram. 
