The pistil of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) is comprised of two fused carpels. The stigma is bilobed, papillose, and at maturity is covered with a sticky exudate. The style is solid. Both stigma and style are made up of four tissue elements-epidermis, cortex, vascular, and transmitting tissue. Transmitting tissue in this species is chlorophyllous. Transmitting cells have thin primary walls and are separated by massive deposits of denselystaining amorphous material. The cells contain numerous mitochondria, dictyosomes, RER, amyloplasts, ribosomes, as well as crystal-containing microbodies and myelin-like formations. Observations are discussed in relation to other reports dealing with similar cell populations.
Young flower primordia of Nicotiana tabacum 'Wisconsin 38' have been successfully cultured on a nutrient medium supplemented with kinetin. The petal, stamen, and carpel primordia form in the normal acropetal sequence during the first week on excised floral apices which initially bore only sepal primordia. Relatively normal morphogenesis of the organs ensues, and on optimal concentrations of kinetin, pedicel length, calyx length and width, corolla width, and ovary length and width after 4 weeks were comparable to those in the normal flower at anthesis. The corolla, filaments, and style were always much shorter than normal. Large quantities of pollen were produced on low kinetin concentrations and normal embryo sacs formed in the numerous ovules. When kinetin was omitted from the medium, similar explants initiated all the organ primordia, but these subsequently remained minute through 4 weeks of culture. The data indicate that organ initiation is independent of exogenously supplied hormones, but that the later phases of bud growth have a marked requirement for kinetin. It is suggested that the sepals or petals may provide some stimulus for the initiation of meiosis in the anthers and ovules. In that flower morphogenesis in culture is independent of specific regulation from the rest of the plant, bud development appears to be relatively autonomous.
In view of the lack of information on the anatomy of rooting in vitro, the time course of adventitious rooting was followed in an apple rootstock. Microcuttings raised on Murashige–Skoog medium were transferred to medium containing indolebutyric acid, then fixed at 0, 1.5, 3, 5, 7, and 10 days. A variety of tissues in close proximity to the cut stem surface exhibited an "activation" response over the first 3 days. Root meristemoids consisting of densely staining cells with enlarged nucleoli formed outside the xylem by day 5. Considerable variation in meristemoid development was noted within single stems and among stems. Meristemoids transformed into root primordia, some of which established a vascular connection with the stem by day 10.
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