216 MORPHOLOGY OF THE ANGIOSPERMS 



Cabomba, two of the three or four ovules are borne on the side walls, 

 near or below the center of the carpel, the others similarly above (Fig. 

 85B). Horizontal veinlets extend from the midrib and from the laterals 

 across the carpel side just above the ovules, and the ovule traces are 

 derived at the point of anastomosis of each pair. This has been de- 

 scribed as "suspended by the sling method." In Brasenia, the vascular 

 system is similar, but the ovule trace is derived at the point of union 

 of the midvein and a transverse veinlet; the ovules, therefore, are borne 

 along the midvein. In Nelumbo, the ovule is attached along the ventral 

 suture, deriving its trace in the "sling" fashion at the point of union of 

 horizontal veinlets which connect two "posteriolaterals." Cerafophijllum 

 has a solitary ovule attached along the dorsal vein. In these four genera, 

 the placentation is clearly modified laminar (Fig. 85). Some of the 

 Magnoliaceae (Michclia) also show reduction of laminar placentation 

 — ovule supply from both dorsal and ventral veins. 



Morphological Nature of the Carpel 



The problem of the fundamental nature of the carpel — axial or ap- 

 pendicular — leads far back in the history of vascular plants, back to 

 the differentiation of the ancient, thalloid plant body. Because of 

 similarity in form and structure, the leaflike nature of the carpel has 

 been recognized since the earliest days of plant study. Detailed com- 

 parative studies in ontogeny and anatomy, especially those of nodal 

 structure, have shown that the similarity is much closer than had been 

 believed; that many supposed differences in position, origin, and de- 

 velopment of these organs are based on misinterpretations. Discussion 

 of the possible homology of carpel and leaf has been prominent in 

 botanical history. The carpel has been called a fertile leaf, and the leaf, 

 a sterile sporophyll. Leaf and sporophyll have been called organs sui 

 generis. The theory of phyllospory and stachyospory has added the new 

 term stegophylls for carpels that "surround" and "protect" stachyo- 

 sporous ovules. Interpretation under this theory implies that the ap- 

 pendages commonly called carpels are of two basically different types 

 — foliar and cauline — an interpretation that is unacceptable by morphol- 

 ogists. In 1956, the interpretation of the carpel as a leaflike appendage 

 was challenged again; it was considered axial, a part of the receptacle, 

 on which are borne "buds," the ovules. In support of this view, the 

 phyllospory-stachyospory theory maintains : 



1. The inversion of bundles has no significance. The inversion is 

 merely the "aberrant result" of the "moving inward" of a vascular bundle 

 to a part radially inward from its point of origin. 



2. Pairs of normally oriented bundles in the ovary wall — as in parietal 

 placentation — are merely "two adjacent bundles." 



