CHAPTER XV 
PLAN AND STRUCTURE OF THE FLOWER AND ITS 
ORGANS 
208. Parts or Organs of the Flower. — Most showy 
flowers consist, like those studied in the preceding chap- 
ter, of four circles or sets of organs, the sepals, petals, 
stamens, and pistils. The sepals, taken together, consti- 
tute the calyx; the petals, taken together, constitute the 
corolla (Fig. 158).1. Some- 
times it is convenient to have 
a word to comprise both calyx 
and corolla; for this the term 
perianth is used. <A _ flower 
which contains all four of 
these sets is said to be com- 
plete. Since the work of the 
flower is to produce seed, and 
seed-forming is due to the 
Fic. 138.— The Parts of the Flower. 
cooperation of stamens and cal, calyx; cor, corolla; st, 
. . P : il. 
pistils, or, as they are often stamens ; p, pisti 
called from their relation to the reproductive organs of 
spore-plants, microsporophylls and macrosporophylls (see 
Sect. 374), these are known as the essential organs 
(Fig. 138). The simplest possible pistil is a dwarfed and 
t The flower of the waterleaf Hydrophyllum canadense, modified by the 
omission of the hairs on the stamens, is here given because it shows so plainly 
the relation of the parts. 
197 
