INTRODUCTION 
commonly elongated, the floral leaves, or some of them, being given off 
from it in a spiral. In higher types the development of the axis is arrested 
and the floral leaves become whorled. The number of whorls is typically five, 
and there are commonly either five or three leaves in each whorl, though 
many modified arrangements occur. Thus, whilst the Stone-crop has five 
sepals, five petals, ten stamens, and five carpels, and the Wild Hyacinth 
three outer and three inner perianth-leaves, six stamens, and three carpels, 
an indefinite number of stamens is common, as in the Buttercup and the 
Rose; five occur in many plants; the carpels may be indefinite in number, 
as in the Mousetail, the Buttercup, and the Rose, or are commonly reduced 
in number to three, as in the Violets; two, as in Nightshade ; or one, as 
in Plums and in the Pea Family. In the Enchanter’s Nightshade {Circled) 
there are four whorls of two leaves each, i.e. two sepals, two petals, two 
stamens, and two carpels. 
As a rule, the leaves of each whorl are alternate with those of the 
preceding whorl, the petals being opposite the spaces between the sepals 
and the outer row of stamens opposite the spaces between the petals. Prim- 
roses and Irises are marked exceptions to this rule, the five stamens of the 
former being opposite to or superposed to the petals, and the three carpels of 
the latter superposed to the three stamens. Such exceptional cases may 
generally be explained by a whorl of stamens having become suppressed. 
Where the floral leaves in each whorl are similar in size and shape, the 
flower can be divided symmetrically in several directions or planes intersect- 
ing in its centre, and is termed poly symmetric. Where the floral leaves are so 
unequal that, as in a Pea or Orchid, the flower can only be so divided in 
one direction, it is monosymmetric ; whilst when it cannot be symmetrically 
divided in any direction, as in the Valerians, it is asymmetric. 
The arrangement of the floral leaves upon the floral receptacle, and the 
modification of the latter, produce differences in what is called the insertion 
of the parts of the flower which are very important in the 
Natural System of classification. If sepals, petals, stamens, 
and carpels spring one beneath the other from such a more or less conical 
receptacle, as in the Mousetail, Buttercup, or allied plants, the calyx is 
Insertion 
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