THE CARPEL 



211 



only one ovule, has a reduced vascular supply, consisting of simple, 

 unbranched dorsal and ventral bundles (Fig. 85C). The ovule is de- 

 scribed as "borne on the dorsal bundle." Though illustrations show no 

 vascular trace, the ovule lies directly over the dorsal bundle and 

 seems to represent a last stage in reduction from laminar placentation. 

 These three genera apparently show derivation of few-ovule placenta- 

 tion directly from the laminar type. In contrast, in carpels with one or 

 two ovules in apocarpous Rosaceae and Ranunculaceae, basal placenta- 

 tion is clearly reduced from submarginal (which, in turn, has been 

 derived from laminar placentation) (Fig. 42). 



Fig. 85. Diagrams of ovaries showing reduced laminar placentation. A, Brasenia, two 

 ovules at union of midvein and lateral veins; B, Cabornha, three to four ovules 

 on transverse veinlets; C, CciatopJujUum, vascular supply reduced, remnants of 

 dorsal and ventral bundles; D, Nelumbo, ovule solitary, attached at union of lateral 

 veins. (A, B, D, adapted from figures arid descriptions of Strasburger and Saunders; 

 C, after Eckardt.) 



Further evidence that laminar placentation is primitive is seen in the 

 Butomaceae and Hydrocharitaceae, families in which this type of 

 placentation is associated with open carpels and, in the Butomaceae, 

 with decurrent stigmas. Laminar placentation, though little discussed, 

 has been considered a specialized, rather than the primitive, type, a 

 form derived from "marginal" by increase in the fertile area of the 

 sporophyll. But the presence of the laminar type in primitive families 

 of both dicotyledons and monocotyledons and of transitional forms in 

 the Ranales and Cabombaceae supports the view that placentation in 

 the angiosperms was primitively laminar. 



In greatly reduced placentation, interpretation of ovule position may 

 be difficult; evidence from anatomy, ontogeny, and comparison with 



