THE CARPEL 235 



marginal, are connate laterally or by their ventral margins, the placentae 

 lie near together around a central point (Fig. 84B) — sometimes around 

 the prolongation of the receptacle (Fig. 88A). This is axile placenta- 

 tion, frequently incorrectly called axial. The term axial implies that the 

 placentae are borne on the axis or are a part of the axis, an old view 

 still sometimes maintained, but, as shown by evidence from anatomy 

 and ontogeny, and comparisons with related taxa, this is incorrect. No 

 placentae are morphologically cauline. 



Axile placentation has been commonly considered the primitive type 

 — in some interpretations, more primitive than laminar — from which 

 other types have been derived. It is surely a primitive type in syncarpous 

 gynoecia, the type from which free central and some forms of basal 

 and suspended placentation have been derived; the type commonly 

 called parietal has probably not been derived from axile. 



The term parietal has long been applied to placentation where the 

 ovules are borne "on the wall" of the ovary, as the word implies. 

 Though usually applied only to placentation in syncarpous ovaries, it 

 has also been applied to placentation in free carpels, and its use in 

 this way has been considered desirable for placentation in free, follicu- 

 lar carpels. But all placentae are borne morphologically "on the wall" 

 and are foliar, not cauline, and terms indicating merely a laminar 

 position are not sufficiently specific. In syncarpous, unilocular gynoecia, 

 the ovules are usually borne in longitudinal rows — a typical parietal 

 placentation. There are two interpretations of the origin of this placenta- 

 tion, which is obviously double in nature: (1) that the placentae repre- 

 sent axile placentae, withdrawn from their original central position by 

 reopening of the carpels and retraction of their margins; (2) that the 

 placentae have been formed by the bringing together of margins and 

 submarginal placentae of open carpels in the development of syncarpy. 



In syncarpous gynoecia that are formed by the union of open carpels, 

 margin to margin, the submarginal placentae of adjacent carpels are 

 brought close together and fuse to form a two-lobed placenta or, when 

 fusion is intimate, a structurally simple (morphologically double) pla- 

 centa. This fusion of parts of different carpels to form a single structure 

 that may show no histological evidence of this compound nature is 

 repeated in the vascular tissue. The two ventral bundles may lie near 

 together, so that the placenta has a double vascular supply; they may 

 fuse to form a two-lobed bundle or may form a simple bundle. All stages 

 in the union of the bundles are found in cross sections of typical 

 syncarpous ovaries with parietal placentation. All these bundles, like 

 the dorsal bundles, are normally oriented with xylem toward the in- 

 side, the vascular structure to be expected if fusion of adjacent carpels 

 is, morphologically, margin to margin. Under the theory that the uni- 



