STRUCTURE OF THE FLOWER AND ITS ORGANS. 143 
as the essential organs, Fig. 116. The simplest possible pistil 
is a dwarfed and greatly modified leaf ($ 188), adapted into 
a seed-bearing organ. Such a pistil may be one-seeded, as in 
Fig. 169, or several-seeded, as in the right-hand part of Fig. 
171; it is called a carpel. The calyx and corolla are known 
Fic. 116.— The Essential Organs. 
A, stamens and pistil of a tulip (the perianth removed) ; s, stamens; p, pistil; 
B,aseparate stamen, with its anther a discharging pollen; /, the filament ; 
C, pollen-grains. 
as the floral. envelopes. Flowers which have the essential 
organs are called perfect flowers. They may therefore be 
perfect without being complete. In cases where the perianth 
contains only one row of parts, it is assumed 
that the petals are lacking. Such imperfect 
flowers are said to be apetalous, Fig. 117. 
176. Regular and Symmetrical Flowers. 
—A flower is regular if all the parts of 
the same set or circle are alike in size and 
shape, as in the stonecrop, Fig. 118. Such 
flowers as that of the violet, the monkshood, 
P : Fic. 117.—Apetalous 
the nasturtium, or the laburnum, Fig. 119, — Mowerof European) 
are irregular. Symmetrical flowers are Wild Ginger. 
those whose calyx, corolla, circle of stamens and set of carpels 
consists each of the same number of parts, or in which the 
