28 OUTLINE OF STRUCTURAL BOTANY 
is more distinctly shown in the buttercup petal than it is in many 
flowers. (Fig. 34.) 
These five petals appear at first to be arranged in a circular 
line, each occupying an equal space in the circle, but if we shave 
the flower as before and examine with care we find that they over 
ride one another in a broken spiral as seen in the diagram, Fig. 36. 
As in the case of the arrangement of the stamens, this disposition 
of the petals may not hold for other flowers although it is typical 
of many. In the flowers of the lily, for example, three petals 
occupy each a portion of a circle while the three other petaloid 
members of the bell, in fact sepals, occupy a circle beyond these. 
As also in case of stamens, in “irregular” flowers the petals 
may assume positions not at all typical. Thus, in the flower of 
the sweet pea three of the petals are situated much to one side, 
while a fourth, which is in fact a union of two, occupies much of 
the other side. 
Leaving the petals and examining our buttercup flower further 
we find inserted into the base of the receptacle, in a ring outside 
the petals, the five green sepals. (Figs. 28, 32.) These are ar- 
ranged about the base of the receptacle in much the same order as 
the petals, one overlapping the other to a certain extent, but alter- 
nating with the petals. 
Thus we have the four elements of the complete flower arranged 
in four series from within outward in the order, the pistil, the 
stamens, the petals and the sepals; the petals forming the corolla, 
the sepals the calyx. | 
But while these four sets of organs ‘are generally in this order 
they are not always thus disposed, for in certain cases the stamens 
are inserted, not in‘a circular group next to the pistil but upon the 
base of the petals and again, they may find this insertion upon 
the calyx. So also the calyx and corolla may seem to arise, not 
from below the base of the pistil but from above the rounded base. 
Such peculiarities are important as characteristics in the classi- 
fication and description of the flower and should be carefully 
observed. 
When the whorls of stamens and petals are arranged below the 
pistil and free from it they are technically said to be hypogynous. 
(Fig. 38), and as this term is much used in botanical works it is 
a good one to remember as is also the term epigynous (Fig. 40) 
which is applied when the calyx, corolla and stamens seem to grow 
at the summit of the rounded base of the pistil, the ovary, as is 
the case with the rose where the ovary forms a gracefully oval base 
