COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. III. POMOIDEAE: CRATAEGUS, HESPEROMELES, MESPILUS, OSTEOMELES

The carpels in Crataegus, Hesperomeles, Mespilus, and Osteomeles appear to constitute a morphologically related group: all have bony pits, ovules that tend to be acollateral (usually superposed), and clearly separate ovular and wing bundles, i.e., no "ventral" bundles, at the level of ovular insertion. In species whose carpels have no sutural opening, the integuiments are more extensively fused with one another, the degree of intercarpellary fusion tends to be greater, and the carpels are fused with the floral cup to relatively higher levels than in those species whose carpels have a sutural opening. In the few cases in which wing and ovular bundles are adnate at the locular base (Crataegus monogyna, Mespilus, Osteomeles anthyllidifolia, 0. schwerinae), the extent of interand extracarpellary fusion and sutural closure is among the most advanced. THE PRESENT study initiates an analysis of carpel morphology in the rosacean tribe, Pomoideae. In earlier investigations (Sterling, 1964a, 1964b), the structure of the prulnoid carpel was considered, with the resulting documentation of 4 prinicipal phylogenetic trenids: (1) complete fusion of 2 integuments to a single massive one; (2) reduction in the number of vascular bundles in the base of the carpel; (3) reduction in prominence of the ovular bundles; and (4) progressive acropetal fusion of the ovular bundles with one another and with the wing bundles. These trends accompany the progressive closure of the carpellary suture, anl event that was choseni on a priori grounds as a primiary evolutionary development. The miiembers of the Pomoideae appear to constitute a closely related group. They share a commoln polyploid base number of 17 (Moffett, 1931), occasionally 16 (Sax, 1931). Intergeneric hydrids are well known (Sax, 1931, 1933; Ferniald, 1947). The fruit is almost invariably a pome. In all but the miulti-ovulate genera, the ovules are erect, anatropous, and apotropic (i.e., their funiiculi are ascending, their chalazae are directed away from-l the placenta, and their micropyles face the base of the locule). One the basis of the histology of the pit of the mature fruit, i.e., whether that structure is cartilaginous or osseous, Lindley (1822) divided the pomoid geniera into 2 primary groups. The same major classification has been followed by Pechoutre (1902) and Rehder (1947). Although other investigators (Decaisne, 1874; Focke, 1894) have used different features for a primary differentiation, the grouping of Linidley will be followed I Received for publication December 21, 1963. This study was aided by grant G-16142 from the National Science Foundation and by a Fellowship grant from the John Simon Guggenheim Memorial Foundation. Dr. Maxine Thompson prepared many of the slides used in this research. in this study because it appears to be in accord with other morphological evidence. Among the Pomoideae with "bony" carpels, the genera Crataegus, Hesperomeles, Mespilus, and Osteomeles seem to share a common carpellary construction. (Indeed, Mespilus and Crataegus are frequenitly regarded as being closely related on other grounds.) Consequently, it seems reasonable to examine their carpels for indications of evolutionary trends. MATERIALS AND METHODS-The species used were Crataegus douglasii Lindl., C. mollis (T. & G.) Scheele, C. monogyna Jacq., C. nigra W. et K., C. oxycantha L. var. paulii Rehd., C. stipulosa Stend., C. suborbiculata Sarg., C. tanuphylla Sarg., C. tennowana A. Nels.; Hesperomeles ferruginea (Pers.) Benth., H. glabrata Roem., H. heterophylla Hook., H. incerta (Pittier) Maguire, H. latifolia (HBK.) Roem., H. oblonga Lindl., H. obovata (Pittier) Standl., H. obtusifolia Lindl.; Mespilus germanica L.; Osteomeles anthyltidifolia Lindl., 0. schwerinae Schneid., 0. subrotunda C. Koch. Floral specimens were kindly provided by the herbaria of the University of California (Berkeley, Davis), the herbarium of the University of Vienna, and the herbarium of the Royal Botanic Gardens at Kew. The methods of preparation were described earlier (Sterling, 1964a). RESULTS-To simplify the descriptions and to miinimize repetitive details, certain conventions will be followed. The base of the carpel will be regarded as being situated just above the insertioni of the staminal bundles. This level will be the starting point from which the observer proceeds upwardly into the carpel. The observer's upward movement becomes translated ilnto movement of the entities that he observes as he goes to each progressively higher transectional level. Thus, a bundle which is in the vascular cylinder below and in the outer cortical region higher up will be described as ascending and departing centrifugally from the vascular cylinder. A bundle which is