CHAPTER XV 



PLAN AND STRUCTURE OF THE FLOWER AND ITS 

 ORGANS 



St., 



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. 138).i Some- 

 tiitnes 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 

 cooperation of stamens and 

 pistils, or, as they are often 

 called from their relation to the reproductive organs of 

 spore-plants, mierosporophylls and macrosporophylls (see 

 Sect. 374), these are known as the essential organs 

 (Fig. 138). The simplest possible pistil is a dwarfed and 



1 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 



cal'- 



FlG. 138. 



The Parts o£ the Flower. 

 cal, calyx; cor, corolla; st, 

 stamens ; p, pistil. 



