254 



STRUCTURE AND VITAL PROCESSES OF PLANTS 



I. II. 



Fig. 235. — I. Diagram of a radial flower 

 (Iris). II. Diagram of a zygomorphic 

 flower (Pea). 



4. Floral Diagram. — Now, if we draw four or tive con- 

 centric circles and mark the horizontal sections of the several 



tloral leaves in their correct relative positions, 

 we obtain something like the ground plan of the 



flower, and what in Botany 

 is called the floral diagram 

 of that plant. The conven- 

 tional way in which the 

 ditierent parts should be 

 drawn is shown in the ad- 

 joining illustration. As these 

 diagrams show at a glance 

 the number and relative 

 position as well as the cohe- 

 sion and adhesion of the 



different floral parts, they are very useful to a student of 



Botany. 



5. The Receptacle. — If a flow^er is cut longitudinally 

 through its centre, and the parts of the section are drawn, we 

 obtain some- /~\ 

 thing like the >^ ^^ ^-\ \ J^ 

 elevation of the 

 structure of 

 that flower, as 

 shown in flg. 

 2 3 6. This 

 diagram does 

 not exhibit the 

 number or co- 

 hesion, but the 



relative adhesion of the several floral parts, and, in particular, 

 it shows tlieir position in relation to the floral receptacle. This 

 is the more or less enlarged top of the flower-stalk. Take, for 

 instance, the flower of a Toppy or of a Custard Apple, and make 

 such a longitudinal section. You will liiid that tlie sepals, the 

 petals, the stamens, and tlic pistil, all rest on the slightly bulged 

 surface of the receptacle. In the Custard Apple this receptacle 



Pig. 236.— Position of ovary: 1. superior, 

 '6. half-superior. 



