ANTHERIDIAL FORMATION IN ONOCLEA SENSIBILIS L.: GENESIS OF THE JACKET CELL WALLS

Antheridial initiation in Onoclea sensibilis L., an advanced leptosporangiate fern, begins with the production of a small, wedge-shaped cell within the anterior region of the vegetative cell. This is in contrast to previous reports claiming that the initials are formed by a localized protuberance in the cell wall ofthe vegetative cell (Campbell, 1886; Davie, 1951; Leung and Naf, 1979; Nayar and Kaur, 1971). The mature antheridium of Onoclea is composed ofthree uniquely shaped jacket cells surrounding spermatogenous cells. The two funnel-shaped jacket cell walls are shown to form in a lateral circular manner. Except for the production of the antheridial initial cell, jacket cell formation in Onoclea proceeds in accordance with the classical concept of antheridial development in advanced ferns accredited in part to Atkinson (1894), Campbell (1886), Kny (1869), and Strasburger (1869). The classical concept has been contested in more recent years by Davie (1951), Leung and Naf (1979), and Verma and Khullar (1966). MATURE ANTHERIDIA of most advanced leptosporangiate ferns, including Onoclea sensibilis L., are composed of three uniquely shaped jacket cells. The jacket cells are formed during the first four divisions in an antheridial initial, resulting in a basal cell, which varies in shape depending on the species; a doughnut-shaped ring cell; and a disc-shaped cap cell surrounding two spermatogenous cells. The morphology of the mature antheridia has been well documented (Atkinson and Stokey, 1964; Davie, 1951; Nayar and Kaur, 1971), but the genesis of the jacket cell walls remains controversial. Four concepts of jacket cell development in advanced leptosporangiate ferns have been reported in the literature: the classical concept attributedto Atkinson (1894), Campbell (1886), Kny (1869), and Strasburger (1869) by Verma and Khullar (1966); Davie's concept (Davie, 1951); Verma and Khullar's concept (Verma and Khullar, 1966); and a recently proposed concept by Leung and Naf (1979). A concept attributed to Stone (1958,1961,1962) by Verma and Khullar (1966) is considered by this author to be synonymous with the classical concept. The points of contention among the authors concern the orzentation of the phragmoplast, the pattern of cell wall deposition, and the orientation of the new cell wall during ' Received for publication 13 July 1984; revision accepted 23 October 1984. 2 Present address: Department of Biology, 130 College Place, Syracuse University, Syracuse, NY 13210. Microscopy was accomplished in the Bessey Microscopy Facility, Iowa State University, Ames. I wish to thank Drs. Donald R. Farrar and Harry T. Horner, Jr., for critically reviewing the manuscript. each division in the formation of the jacket cells. All previous authors have agreed that the initial cell of the antheridium is formed by a localized protuberance in the vegetative cell followed by a periclinal cell division (Fig. 1A, B, C). The classical concept then states that the first cell division in the initial is either transverse, concave, or funnel-shaped. The second division is hemispherical (curved, periclinal), and the third division is funnel-shaped (Fig. 1D, E, F). With each division, the cell wall is formed in the same orientation as the preceding phragmoplast. Davie's concept claims that all three divisions are originally transverse, but the firstformed wall may be secondarily displaced downward to ultimately appear concave or funnel-shaped (Fig. 1G, H). The second wall is secondarily displaced upward until it appears as a curved, periclinal wall (Fig. 1I, J). Eventually the second wall comes into contact with the third wall which also may be secondarily displaced downward (Fig. 1K, L), resulting in a final morphology similar to that proposed by the classical concept (Fig. 1F). Verma and Khullar's concept agrees with Davie's concept except that Verma and Khullar (1966) feel the second wall is originally formed in a hemispherical position. Leung and Nafbs concept states that during the first division in the initial, the phragmoplast is oriented transversely, but the subsequent cell wall is deposited in the shape of a funnel. Deposition occurs in a vertical manner, upward and outward from a central basal re-