ANGIOSPERMS. 
6ii 
than on the vegetative shoots. In contrast to the lax mode of expression used by many 
botanists, I understand by Symmetrical Structures those which may be divided into two 
halves, each of which is an exact reflex image of the other. If a flower can be divided 
in this manner by only one plane, I call it simply symmetrical or monosymmetrical ; if, on 
the contrary, it can be symmetrically divided by two or more planes, it is, as the case 
may be, doubly or poly symmetrical. The happy expression zygomorphic already used by 
Braun may be applied equally to monosymmetrical flowers and to those polysymmetrical 
ones in which the median section produces halves of quite a different form from 
those caused by lateral section {e.g. Dicentra). I apply the term regular to a poly- 
FlG. 416.— Zygomorphic flower of Coluvinea Schiedeana : A entire flower after removal of two sepals ; B androecium ; 
C gynseceum ; Z) the coherent anthers magnified and seen from behind; iT horizontal section of the ovary; /^diagram; 
a anthers, n stigma, style, fk ovary, d the staminode developed into a nectary,// the lateral oblique placentae. 
symmetrical flower only when the symmetrical halves produced by any one section are 
exactly like or very similar to those produced by any other section ; or — which comes 
to the same thing— when two, three, or more longitudinal sections divide a flower into 
four, six, or more equal or similar portions. 
In exactly defining the symmetrical relations of a flower, the relative positions of the 
parts, as represented by the diagram, must first of all be distinguished from the entire 
form of the flower, such as is realised in the development of the organs. 
If attention is paid first of all only to the relative positions of the parts, it is clear 
that they can never be distributed symmetrically in flowers with a truly spiral structure ; 
R r 2 
