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. 1 78) and apple. How FIG. i 77 . PISTIL OF 

 . . i > A i GARDEN PEA, the 



many carpels m an apple ? A peach ? stamens being pu]led 

 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 



I 



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. 



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- 



