THE CARPEL 213 



closely related groups, are always appendicular. Interpretation of the 

 basal ovule in free carpels as cauline is nonsensical, especially when 

 applied to stipitate achenes; minute projections of the stem must be 

 assumed to pass through the stipe of each carpel. 



The solitary surviving ovule of a submarginal row is usually the 

 proximal member but may be the distal member, as in Leitneria. Rarely, 

 if ever, is it a median one. The term medion placentation has been used 

 occasionally — apparently always loosely and in a descriptive sense — 

 for ovules borne "in the middle of the lamina," on the dorsal side, on 

 the ventral side, or between these, as in Brasenia and Cabomba. Median 

 has been suggested as a replacement for submarginal and, in "peltate" 

 carpels, as a term to refer to the condition where the solitary ovule is 

 borne on the "cross zone." Median, as a descriptive term for placenta- 

 tion, is hopelessly loose morphologically and should not be used. It has 

 been combined with an even poorer term, lateral — in "median lateral." 

 Both "lateral" and "median" have been applied to ovules borne on the 

 dorsal and ventral edges of the folded carpel and on the lamina between. 

 The vestigial ovules in achenes which are obviously submarginal and 

 ventral have been called "lateral median," and the ovules in achenes of 

 the Ranunculus type have been described as "median lateral." These 

 terms are morphologically meaningless and of doubtful descriptive 

 value. 



Axial, parietal, and free central placentation are discussed under 

 Syncarpy. 



The U-type Placenta. As a part of the demonstration of carpel mor- 

 phology according to the peltate theory, a form of placenta called the 

 U-type has been described and interpreted as "the placentation type of 

 the angiosperms." The interpretation has been the result of the exten- 

 sion of the theory of the underlying peltate nature of floral appendages 

 to greatly reduced carpels, with emphasis on the "cross zone" as a 

 morphologically important part of the organ, especially of the carpel. 

 The U-shaped placenta has been given this name because it surrounds 

 the base of the ventral furrow or slit of a so-called peltate carpel. It is 

 described as present in its typical form in achenes of the Rosaceae and 

 Ranunculaceae, where the ovule is borne at the base of the "slit" — and 

 of the "U" — on the "cross zone," with the arms of the placenta extend- 

 ing upward along the united margins of the carpel. The arms of the 

 placenta, sterile in most of these taxa, may be fertile. The placenta, in 

 these achenes, is merely a position, or area, where the ovule is borne. 



A consideration of placentation in general and the ontogeny and basic 

 morphology of the carpel shows that the U-type placenta is merely a 

 modified form of the submarginal type, a form resulting from advance 

 in carpel closure from ontogenetic to congenital fusion, together with 



