THE INFLORESCENCE, AND THE FLOWER 



263 



and Rock-Roses. In the Grasses, which arc racemose, even upright 

 inflorescences may be dorsiventral. This is seen in the Cock's-foot {Dactyhs), 

 and the Mat-weed (Xardus). 



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. 177, p. 255). 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 fully disclose 

 their position relative one to another. Such 

 facts may be obtained by observation from 

 above, and be plotted into a floral diagram 

 (Fig. 187). This allows of the representation 

 of each constituent part. It also gives the 

 orientation 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 di ^ ar f 7 of Liliaceous 

 the median plane ; that at right angles to it ^Xdrdi A ibove E ^!Snts^ 

 the transverse plane. It is thus possible to jj*j^ the bract is shown below, 



plot the constituent parts in ground plan, and 



to describe them in 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 represent the Sepals, P the Petals, A the Androecium, 

 and G the Gynoecium, the number of parts of each may be added 

 as a numeral (00 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 



