150 



STRUCTURAL BOTANY 



broader above. A petal differs from a sepal in having 

 a well-marked midrib, which projects as a ridge on its 

 outer or lower surface. On either side of this ridge 

 is a deep furrow, into which in the bud the edge 

 of the adjoining sepal fits (see Fig. 56). The side 

 veins of the petal diverge from the midrib, running 

 obliquely upwards and outwards to the edge, these 



FIG. 56. Transverse section across a flower-bud of the White 

 Lily, s, one of the three sepals (unshaded) ; p, one of 

 the three petals (shaded) ; st, one of the six stamens in 

 two whorls of three ; 0, pistil consisting of three carpels. 

 Magnified about 8. (R. S.) 



veins being connected by oblique branches to form a 

 network. At the base of each petal is a honey- 

 bearing groove like that on the sepal. 



The stamens are six in number, in two whorls of 

 three each. The outer whorl is alternate with the 

 petals, and therefore opposite the sepals. The inner 

 whorl is alternate with the outer, and therefore 

 opposite the petals. In fact, all through the flower 



