THE FLOWER 89 



of angiospermy (enclosure of the ovules), a part of the flower. Elabora- 

 tion of the perianth, with the development of two series of organs, took 

 place within the angiosperms. Under a second theory, all perianth 

 parts are considered modified sporophylls. This is an old theory that has 

 received little attention since 1900. The petals in most families have 

 been shown to be sterile, petaloid stamens. But all sepals and the petals 

 of some families, for example, Magnoliaceae and Calycanthaceae, have 

 been shown by transitional forms and anatomical structure to be modi- 

 fied leaves. A third theory is based on the view that the primitive flower 

 was naked, and the perianth developed within the angiosperms as a 

 new structure, accompanying the specialization of the flower. Under 

 this theory, the perianth appeared in early forms as bractlike or scale- 

 like organs, protective in function; these organs were increased in num- 

 ber and size, with elaboration in color and complexity of form. The de- 

 velopment of a distinct upper series, the corolla, was one of the later 

 steps. The flowers of ranalian families may give evidence of the origin 

 of the perianth from bractlike, protective organs. They show variety in 

 number and form of bud-scale-like outer appendages. Etipomatia and 

 Himantandra have one calyptralike organ; other genera, a few small, 

 spirally arranged organs. Trochodendron has a few appendages below 

 a naked flower. The distinction between bracts and sepals is hardly 

 possible in some of these genera. There are probably no strictly peri- 

 anthless flowers — with the exception of those that are greatly reduced 

 in structure, as in the inflorescences of CercidiphijUum and many of 

 the Amentiferae. All stages in the evolutionary development of the 

 calyx from bracts are present in the Ranales and Dilleniales. 



The corolla has probably arisen in two different ways. A perianth of 

 many spirally arranged organs, with gradual transition from bractlike 

 to larger petaloid members — as in the Magnoliaceae, Calycanthaceae, 

 Himantandraceae, Nymphaeaceae — apparently became separated into 

 proximal and distal parts, the distal more petaloid and otherwise dis- 

 tinct from the proximal. Stages in this specialization are present in the 

 Magnoliaceae. The genus Magnolia itself shows reduction in number 

 in the members of the perianth, with gradual change from spiral to 

 whorled arrangement (Fig. 41A to C). Some species show definitely 

 distinct corolla, as does the allied genus, Liriodendron (Fig. 41D to F). 

 In the corolla, stages in transition from spiral to whorled arrangement 

 are frequent, and there may be two whorls of petals. A second origin 

 lies in the sterilization and petaloid elaboration of stamens. Anatomy 

 demonstrates that the petals of many families are, in vascular structure, 

 unlike the sepals but like the stamens, regardless of extent of superficial 

 resemblance in form to sepals; the number of traces departing to a petal 

 is like that going to the stamen and unlike that to the sepal. The corolla 



