6ia 



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 symmetricaP. 



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 -<^. But inasmuch as the entire form of the mature flower is essentially deter- 



FlG. 417. — Zygomorphic flower of Polygala gratidiflorn : A entire flower seen from the, side after removal of one 

 sepal k ; B flower divided symmetrically without the gynaeceum ; 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, « 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 Nymphoea 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 

 a smooth edge vertically upon the paper so as to bisect the diagram. 



