88 MORPHOLOGY OF THE ANGIOSPERMS 



nodal areas on the lower part of receptacle, as in Liriodendron (Fig. 

 41F). Where the arrangement of organs is spiral, the phyllotactic spiral 

 is often the same as that of the leaves but may be different, especially 

 where the floral organs are numerous. 



The Sterile Appendages. The sterile appendages are typically of two 

 kinds: sepals, which together form the calyx; and petals, which make 

 up the corolla. These appendages are below the fertile appendages, the 

 calyx below the corolla. (In Eupomatia, petaloid staminodia form a 

 pseudocorolla between the stamens and the carpels.) Sepals and petals 

 commonly differ in form, size, and other characters. In some families, 

 they may be closely alike, as in most of the Liliaceae; in others, transi- 

 tional forms occur, as in the Magnoliaceae. Interpretation of the peri- 

 anth as calyx or corolla may be difficult and unimportant, as in Driniijs 

 and Wintera, where the organs, ranging from two to several, are spirally 

 placed; and where the perianth is represented by only one or few 

 appendages, which serve as a bud-scale-like cap. 



Commonly, sepals are more or less leaflike or bractlike in form and 

 structure, especially in their vascular relations to the stem. Mor- 

 phologically, they are modified leaves. Typically, they stand in whorls, 

 but, in some primitive families, are spirally arranged — Dilleniaceae, 

 Paeoniaceae. They may be petaloid, but this condition usually accom- 

 panies reduction or loss of the petals, as in the Proteaceae. Where 

 greatly reduced, they have the form of minute teeth, scales, bristles, or 

 mere ridges. Cornus shows all stages of calyx reduction in both ex- 

 ternal and internal structure, and some species have no vestige of a 

 former calyx. (Connation and adnation involving sepals are discussed 

 in later pages.) 



Petals are typically laminar and larger than the sepals. They, like 

 the sepals, are, morphologically, appendages of leaf rank. In many 

 families, they represent sterile stamens, but, in some primitive families, 

 they are probably modified leaves (like the sepals), as evidenced by 

 transitional forms and anatomical structure in Magnoliaceae. Petals 

 have great range in size and form, from the large, elaborate organs of 

 some orchids to minute structures; under reduction, they may become 

 scales, bristles, or glands of many forms. Accompanying compacting 

 of the flowers in inflorescence specialization, they are reduced to small 

 size and lose their petaloid appearance. 



Theories of the nature and development of the perianth are closely 

 bound up with theories of the origin of the flower. One theory is that 

 the perianth, at least in part, was preexistent to the flower. In ancestral 

 forms, sterile appendages were associated with groups of sporophylls, 

 as seen in the bracts below the cones of some conifers and the "flower" 

 of the Bennettitales. These appendages became, with the establishment 



