72 ARRANGEMENT OF FLORAL LEAVES 



the vertical plane at right angles to the transverse plane, 

 and, therefore, passing through the middle of the bract 

 and the inflorescence-axis, is described as median. These 

 definitions will be understood more easily if a Pea-flower 

 (fig. 96) be examined. The standard is posterior (nearest the 

 inflorescence-axis), the two keel-petals are ariterior (nearest 

 the bracts) : furthermore, the standard is median in position, 

 as it is inserted in a vertical plane passing through the middle 

 of the bract and the inflorescence-axis : whereas the wings and 

 the two keel-petals, being on each side of the median line, 

 are lateral in position. Thus the standard is median-posterior, 

 the wings are lateral, and the "keel-petals are anterior-lateral 

 (see also fig. 98). 



ACYCLIC AND HEMICYCLIC FLOWERS. 



Many of the remarks made in reference to cyclic flowers are 

 also true of acyclic and hemicyclic flowers. But the defini- 

 tions with regard to the symmetry of cyclic flowers usually 

 do not hold good for hemicyclic and acychc flowers, because 

 the divergences of the various floral leaves are not constant 

 throughout the whole flower. For instance, the sepals may 

 be two-fifths, the petals three-eighths, and the stamens five- 

 thirteenths. This renders it impossible to divide the flower 

 with mathematical accuracy into two equal halves. Never- 

 theless, acyclic and hemicyclic flowers which present the 

 appearance of actinomorphic flowers are usually described as 

 actinomorphic (e.g. Buttercup), and those which resemble 

 zygomorphic flowers are described as zygomorphic (e.g. 

 Monkshood). 



FLORAL DIAGRAMS. 



In order to represent graphically the relative arrangement of 

 the parts of a flower, we construct maps or ground-plans, which 

 are known z.'a floral diagrams. The simplest method of gaining 

 an idea of a floral diagram is to cut across a flower-bud through 

 the sepals, petals, stamens, and ovaries, and then to look down 

 upon the cut surface exposed. The floral leaves will be seen 

 to form successive circles or spirals. Figs 100 and 101 show 

 floral diagrams. The sepals naturally stand at the outside, 

 and the carpels in the centre (compare pages 13, 14). It is 



