THE INFLORESCENCE, AND THE FLOWER 229 



METHODS OF COMPARISON OF FLOWERS. 



No attempt will be made here to describe fully the wide range of 

 difference in construction of Flowers, nor to treat those differences 

 systematically, as a basis for a natural grouping into Families. Such 

 ' details will be left over to Appendix A. It must suffice to illustrate 

 the methods by which such comparisons are most easily presented, and 

 to state the leading factors upon which these differences depend. 

 Certain essential facts of floral construction may be obtained from a 

 median vertical section (Fig. 168, p. 221). This will give the form 

 and proportion of the receptacle, and the relative levels of the 

 successive organs which it bears. But it 

 cannot indicate their number, or their posi- 

 tion relative one to another. These facts 

 may be obtained by observation from above, 

 and be plotted into a floral diagram (Fig. 178). 

 This allows of the representation of each 

 constituent part. It also gives the orienta- 

 tion of the flower relative to the axis and 

 subtending bract. The side next the axis 

 is described as posterior, that towards the 

 bract anterior. The plane including the 

 axis and the midrib of the bract is called 



.floral diagram of Liliaceous 



the median plane ; that at right angles to Flower. (After Eichier.) The 



small circle above represents the 



it the transverse plane. It is thus possible axis ; the bract is shown below, 



r . black. 



to plot the constituent parts in ground 



plan, and to show their relation to these planes. But the floral 

 diagram gives no record of the elevation. Accordingly it must be 

 used in conjunction with vertical sections in order to complete 

 the .study. A compact mode of registering both is found in the 

 floral formula. If S represents the Sepals, P the Petals, A the 

 Androecium, and G the Gynoecium, the number of parts of each 

 may be added as a numeral (oo indicates an indefinite number). 

 Where the Calyx and Corolla are not differentiated, P may stand 

 for Perianth. Where the parts of one category form more than one 

 whorl, this may be shown by giving a separate figure for each. The 

 mutual relations of the parts can be indicated by brackets, thus 

 showing where parts are united. The position of the outer parts 

 relative to the gynoecium is suggested by a line above or below the 

 latter. Other details are sometimes introduced into floral formulae, 



FIG. 178. 

 Floral diagram of Liliaceous 



