24 OUTLINE OF STRUCTURAL BOTANY 
When this is complete it consists of two circles of organs (Fig. 
28). The outer one which is generally, though not always, green 
called the calyx, is almost always divided, either partly or com- 
pletely, into several parts known as sepals. These green sepals are 
well seen in the case of the rose where each becomes more or less 
sub-divided and thus more ornamental. The inner circle of the 
perianth is known as the corolla and when this consists of several 
divisions the parts are called petals. 
In many flowers the petals remain distinct from each other* while 
in other cases the petals are united showing but a single expansion 
since all the members are blended at their edges as we see the union 
in the harebell or in the convolvulus. 
The petals of a flower are in most cases symmetrical as are other 
27 
Fic. 26—Part of a stem of Zanichella. The naked flowers are seen at the leaf 
axils. 
Fic. 27—An incomplete flower, Clematis. The petals are nearly suppressed while 
the sepals are large and colored. 
Fic. 28—A complete flower, Buttercup, with calyx, corolla, stamens and pistils. 
Fic. 29—An irregular flower (Salvia). 
parts of the same flower. For example, the petals of the buttercup 
or of the apple blossom are all alike, one as long and as broad as 
the other and the sepals of the calyx are, in these blooms, similarly 
symmetrical (Fig. 28). Such flowers are called regular.® 
But the parts of the flowers are not always thus symmetrical, for 
example, the petals of the sweet pea flower differ among themselves 
in size and shape, so also the parts of the larkspur and of the 
cypripedium flowers are not all alike. Such flowers are irregular 
(Fig. 29.) 
Flowers may be perfect in the sense that they include both the 
stamens and the pistils yet they may not be complete in the sense 
*Flowers, the corolla of which is composed of separate and distinct petals, are 
known as polypetalous or better, as choripetalous flowers, while flowers, the corollas 
each of which consists of a single member, made by the union of several petals, are 
monopetalous or more correctly gamopetalous. 
5 When the petals are thus symmetrical the flower is technically homochlamedous 
or, in tamiliar language, regular. When the parts are unsymmetrical the flower is 
heterochlamedous, or, irregular, 
