136 



PLANT BIOLOGY 



Fig. 176. — Simple 

 Pistils of But- 

 tercup, one in 

 longitudinal sec- 

 tion. 



leaf as if rolled into a tube ; and an anther, a leaf of which 

 the edges may have been turned in on the midrib. 



The pistil may be of one part or com- 

 partment, or of many parts. The different 

 units or parts of which it is composed are 

 carpels. Each carpel is homologous with 

 a leaf. Each carpel bears one or more 

 seeds. A pistil of one carpel is simple ; 

 of two or more carpels, compound. Usu- 

 ally the structure of the pistil may be de- 

 termined by cutting horizontally across the lower or seed- 

 bearing part, as Figs. 177, 178 explain. A flower may 

 contain a simple pistil (one carpel), as 

 the pea (Fig. 177); several simple pis- 

 tils (several separate carpels), as the 

 buttercup (Fig. 176); or a compound 

 pistil with carpels united, as the Saint 

 John's wort (Fig. 178) and apple. How 

 many carpels in an apple ? A peach ? 

 An okra pod ? A bean pod ? The 

 seed cavity in each carpel is called a 

 locule (Latin locus, a place). In these 

 locules the seeds are borne. 



Conformation of the Flower. — A 

 flower that has calyx, corolla, stamens, 

 and pistils is said to be complete (Fig. 

 173); all others are incomplete. In 

 some flowers both the floral envelopes 

 are wanting : such are naked. When 

 one of the floral envelope series is 

 wanting, the remaining series is said 

 to be calyx, and the flower is therefore 

 apetalous (without petals). The knot- 



Fir,. 177. — Pistil of 

 Garden Pea, the 

 stamens being pulled 

 down in order to dis- 

 close it; also a section 

 showing the single 

 compartment (com- 

 pare Fig. 188). 





Fig. 178. —Compound 

 Pistil of a St. 

 John's Wort. It 

 has 5 carpels. 



