106 STRUCTURAL BOTANY 



tube, which now forms the cavity of the ovary (see 

 Fig. 38, H). We see, then, how it is that the position 

 of the stigmas is alternate with that of the carpels 

 (see Figs. 10, 11, 12, and 13, pp. 20-23). The 

 septum appears rather late, after the development of 

 the ovules has begun (Fig. 38, G, pi). Each placenta 

 grows out between the rows of ovules ; the two pro- 

 jecting walls thus formed at last meet in the middle 

 to form the septum, dividing the cavity into two. The 

 honey-glands, which lie at the base of the two shorter 

 lateral stamens, arise very late in the development of 

 the flower, when all the more important organs are 

 well advanced. 



All floral leaves arise like other leaves, by the 

 growth and division of the more external cells of the 

 growing point. 



b. Structure of the Floral Envelopes 



We will now consider more fully the structure of 

 the various organs of the flower, and the respective 

 parts which they play in the process of reproduction. 

 We will first consider the structure of a sepal. The 

 sepals form the outer protective covering of a flower 

 while it is still a bud. When the flower opens, the 

 function of the calyx in the Wallflower is almost at 

 an end. 



Of all the floral organs the sepals most resemble 

 foliage-leaves. They are, in fact, merely leaves of 

 simplified structure, having less complex functions to 

 perform than the vegetative leaves. 



The sepal has a similar bundle-system to that of 



