COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. II. PRUNOIDEAE: MADDENIA, PYGEUM; OSMARONIA

A survey of species of the prunoid genera, Maddenia and Pygeum, and of the genus Osmaronia has been made. The ovules of all are pendent, campylotropous, and epitropic. In the prunoids, the ovular supply is intimately connected with a central vascular plexus in the base of the carpel; that plexus is absent from Osmaronia. The prunoid carpels are marked by an extensive degree of fusion among the ovular and wing bundles, by fusion of the sutural margins, by fusion of the 2 integuments of the ovule to a single massive one, and by the presence of 3 or 5 well-developed bundles in the base. The carpel of Osmaronia also has a strongly fused bipartite ovular supply, separate bundles of which, however, become very much attenuated before reaching the funiculus; it has independent ovular and wing bundles, completely separate carpellary margins, 2 clearly separate integuments in the ovule, and 6 distinctive bundles in the carpel base. At the funiculus, the wing bundle of Osmaronia is connected with the adjoining weak ovular bundle by a welldeveloped vascular branch. Various particularities in the morphology of Osmaronia lend support to its segregation into a unique tribe, the Osmaronieae of Rydberg. IN CONCLUDING the comparative study of the prunoid carpel (Sterling, 1964), the author has now examined the young carpels of the 3 remaining genera commonly placed in the Prunoideae: Maddenia, Pygeurn, and Osmaronia. It should be noted that Rydberg (1918) removed Osmaronia to the separate tribe, Osmaronieae. The results of the present investigation indicate that such a segregation is justified. However, Osmaronia has been examined in this portion of the study as a concession to other taxonomic opinions, such as that of Focke (1894). A recent study (Sterling, 1963) has already shown that Prinsepia cannot be regarded as a prunoid genus. MATERIALS AND METHODS-The sources of the floral specimens were the herbaria of the University of California at Berkeley and Davis, respectively, and the herbarium of the Royal Botanic Gardens at Kew. The species used were: Maddenia himalaica Hook. f. & Thomas; M. hypoleuca Koehne; M. hypoxantha Koehne; and M. wilsonii Koehne; Pygeum fragrans Merr.; P. glandulosum Merr.; P. megaphyllum Merr.; P. preslii Merr.; P. topengii Merr.; and P. vulgare Merr.; Osmaronia cerasiformis (T. & G.) Greene. As far as possible, flowers were taken at the same stage of development, namely, unfolding of the petals. The methods of specimen preparation have been described earlier (Sterling, 1964). RESULTS-Maddenia-According to Focke (1894), the genus is dioecious, and the pistillate flowers are bicarpellate. However, Koehne (1911) found that in the Chinese species, at least, the I Received for publication July 19, 1963. This investigation was aided by funds from the National Science Foundation, given under grant G-16142. The microtechnical work was performed by Dr. Maxine Thompson. It is a pleasure to thank both the Foundation and Dr. Thompson for their help. flowers are perfect and monocarpellate. The writer has examined all the specimens of Maddenia in the herbaria of the University of California at Berkeley and the Royal Botanic Gardens at Kew, with the same results: all species, including M. himalaica, have perfect flowers that are predominantly monocarpellate. Each carpel has 2 monotegmic ovules which are pendent, campylotropous, and epitropic. The carpellary margins are fused throughout the length of the ovary. Although the commissural suture is marked externally by a slight cleft along the ventral surface of the ovary, internally the ventral ovarian surface is smooth from the base of the locule up to the level of ovular attachment. Upwards from this level to the top of the locule, a linear groove is evident on the internal ventral surface. (This groove is fairly deep in M. hypoleuca.) A short distance above the insertion of the staminal traces, the center of the vascular cylinder is occupied by a sparse vascular plexus (Fig. 1, 2). At flowering, that plexus is still procambial. The vascular cylinder that supplies the carpel may be composed of 5 main bundles (M. himalaica, M. hypoleuca), or only of 3 large bundles (M. hypoxantha, M. wilsonii). When 5 bundles are present they are the dorsal bundle, 2 wing bundles, and 2 inner vegetative bundles next to the ovular supply.2 The bipartite ovular supply lies between the wing bundles, close to the sagittal plane. Xylem and phloem in the dorsal, wing, and inner vegetative bundles are radially collateral. However, in the ovular supply the xylem and phloem are almost tangentially collateral at the sagittal plane, with the phloem of each half directed toward the phloem of the other. These phloic 2The terminology used here has been explained by Sterling (1964).