THE CARPEL 217 



3. The vascular systems supplying ovary wall and placenta are 

 independent. 



4. The recent recognition of the two-trace nature of the primitive 

 angiosperm leaf breaks down the homology of carpel and leaf, for the 

 carpel is a three-trace organ. 



5. The sessile nature of carpels is evidence that the carpel is axial, a 

 part of the receptacle. 



6. The placenta is an independent structure, also of axial nature, 

 bearing "terminal buds" (ovules). 



In support of the appendicular theory, are the following facts: 



1. The inversion of the lateral bundles is clearly the result of up- 

 turning and inrolling of the sides of laminar organs; they do not arise 

 inverted but are inverted during their course to the carpel or within the 

 carpel base. Similar inverted bundles are common in petioles, where 

 there has been a rolling of the margins and a flattening. Inverted bundles 

 are also found in many veins in cylindrical and rolled leaves of xero- 

 phytes. 



2. The pairing of normally oriented bundles in a syncarpous ovary 

 wall is not a mere "happenstance." The pairs are the ventral bundles of 

 adjacent carpels, fused margin to margin, as open and partly upfolded 

 laminar carpels. The bringing together is ontogenetic in some taxa; 

 congenital in others. 



3. Independence of vascular systems of ovary wall and placenta is 

 normal; the traces which supply these parts arise at different levels on 

 the stem and wholly independently. (They may be freely connected by 

 small veins.) If carpels are to be interpreted as axillary on this basis, 

 so are leaves and all other floral organs in which there are several traces. 

 In laminar placentation, there is no distinction of vascular "systems." 



4. The dorsal trace of the carpel is frequently double; the stamen, in 

 some families, has two traces; the cotyledon, in most families, has two 

 or four traces and shows the origin of the three-trace condition by fusion 

 of the median two (Chap. 9). Anatomically, carpel and leaf are now 

 brought even closer together. (Recognition of the two-trace node as 

 primitive has replaced the long-held theory tliat the three-trace node was 

 primitive. ) 



5. The carpel in primitive families, both monocotyledonous and 

 dicotyledonous, is stipitate; the sessile carpel is specialized. 



6. The placenta is merely a location on the carpel where ovules are 

 borne and where, often, the fertile area becomes enlarged. It appears to 

 be an independent structural part only in highly specialized ovaries 

 where greatly enlarged or where lateral-wall connections have been lost, 

 as in free central and basal placentation. Where enlarged, it has no 

 uniform pattern of vascular supply, as an independent axis would 



