THE CARPEL 249 



and, internally, the vascular systems are united, with little or no evi- 

 dence of the fusion. Similarly, organs in closely placed whorls are so 

 fused that the vascular traces of organs in different whorls become 

 united; the traces of sepals, petals, and stamens that lie in or near the 

 same radius of the flower may be fused and form a single vascular 

 bundle. This morphologically compound bundle may show structural 

 evidence of compound nature, but is commonly simple. Comparisons of 

 the vascular structure of the inferior ovaries of many families demon- 

 strate stages in the fusion of the traces of the appendages and the 

 appendicular nature of inferior ovaries in general. 



In the genus Rosa, the basal part of the receptacle is an invaginated 

 receptacle, with the carpels borne on the surface near the bottom of the 

 hollow center; the distal part is appendicular, consisting of the bases of 

 sepals, petals, and stamens ( Fig. 95B ) . The location of the line between 

 the two parts — where the stelar bundles bend downward — varies with 

 the species. 



The collarlike or cup-shaped structure on which perianth and androe- 

 cium are borne and which surrounds or caps the gynoecium is com- 

 monly called in taxonomy the hypanthium. The term calyx tube — com- 

 mon in the older literature — is correctly applied only to the connate 

 bases of sepals; as applied to the hypanthium, it is obviously morpho- 

 logically incorrect, because it implies that, structurally, the hypanthium 

 consists of appendages borne on other appendages. Under the axial 

 theory of the nature of the inferior ovary, the hypanthium is considered 

 basically axial, consisting of the rim of the receptacle; under the ap- 

 pendicular theory, it is considered to consist of the fused bases of sepals, 

 petals, and stamens. Stages in the evolutionary development of the cup- 

 shaped hypanthium are frequently seen. The Rosaceae provide a good 

 example. In apocarpous genera, Frogaria and species of Riibus, the 

 hypanthium is a flat disc around a convex receptacle; in other species of 

 Rubus, in Spiraea, and Physocarpus, it is a shallow cup around a flat re- 

 ceptacle; in Agrimonia, it is a deep cup, with incurved top, around a 

 flat receptacle. In syncarpous genera, the hypanthium is a shallow epi- 

 gynous cup in Aronia and Amelanchier, a deeper epigynous cup in Pyitis 

 and Cydonia. The Rosaceae also show stages in the adnation of the 

 hypanthium to the carpellary walls. This fusion ranges from slight in 

 Spiraea, to part way up in Sorbiis, to the top of the ovary in most 

 Pomoideae. 



Morphologically, the term hypanthium is loose; it covers complex 

 and varied structures. Usually it indicates a part of the flower that con- 

 sists of the adnate bases of sepals, petals, and stamens. The fusion is 

 not evident externally, and the hypanthium has been commonly in- 

 terpreted as a part of the receptacle, but anatomy shows its true com- 



