-The ontogeny of the sporangia of Sphaeropteris cooperi was studied using cleared whole mounts of sporangia in different stages as well as sori embedded in paraffin and sectioned. The sporangia develop from a single superficial primordial cell that becomes divided into five initials or "segments." Segment 0, located at the level of the surface receptacular cells, does not become subdivided and does not contribute further to the structure of the mature sporangium. Segments I, II, III and IV each become subdivided through a series of divisions to produce the mature sporangia. The four-rowed sporangial stalks are formed from Segment I and part of Segment II, and the capsules develop from a part of Segment II and Segments III and IV. The annulus develops in Segments II and IV. The developmental pattern of the sporangia of Sphaeropteris cooperi is compared to that of the sporangia of higher leptsoporangiate ferns. The most familiar and most frequently illustrated leptosporangia are those of the higher leptosporangiate ferns. The development of the sporangia of the higher leptosporangiate ferns was described in a series of papers (Wilson,1958a, b, 1960) and is now well understood. In the sporangia of the advanced leptosporangiate ferns, as illustrated by species in the Polypodiaceae, Grammitidaceae, and Vittariaceae, it was shown that the stalk and the capsule of the leptosporangium develops from a single epidermal primordial cell that becomes divided into five initials or "segments," rather than from the activity of an apical cell. Each one of these "segments" in turn divides, through a series of divisions to produce the mature sporangium. Segment 0 contributes only to the formation of the stalk; Segment I to a portion of the stalk and part of the proximal face of the capsule; Segment II to the stomial region, the stalk, and to the proximal and distal faces of the capsule; and Segments III and IV to the rest of the annulus and to both the proximal and distal faces of the capsule. Although the stalk may be one-, twoor three-rowed at its base, the capsule is always subtended by a three-rowed stalk. The one-rowed stalk results directly from the horizontal orientation of the first division of the sporangial initial, whereas the twoand three-rowed stalks depend on the orientation of both the first division and also the division that produces Segment I. A review of the history of our knowledge of the nature of the leptosporangium and its development was published in the introduction to the study of the ontogeny of the sporangia of Phlebodium aureum (L.) J. Sm. (Wilson, 1958a). Recent descriptions of sporangial development continue to reproduce the erroneous pattern apparently originated by Campbell (1905) that the sporangial initial produces a three-sided apical cell that cuts off several basal cells to form the stalk until a transverse division stops its activity by cutting off the cap cell. Other accounts are unclear, incomplete and often incorrect. (see Gifford and Foster, 1989; Bold et.al., 1987; Holttum et. al., 1970). No detailed ontogenetic studies have been published since the appearance of the paper on This content downloaded from 207.46.13.149 on Wed, 28 Sep 2016 06:18:20 UTC All use subject to http://about.jstor.org/terms WILSON: SPORANGIAL ONTOGENY IN SPHAEROPTERIS the sporangium of Anarthropteris lanceolata (Hook. f.) Pic. Serm. (as A. dictyopteris (Mett.) Copel.) (Wilson, 1960). As pointed out in a study of mature sporangia of species of the Polypodiaceae, Grammitidaceae, and Vittariaceae (Wilson, 1959), the cell arrangement in the sporangia reflect the ontogeny of these structures and, with but few exceptions, there is no reason to doubt that the development of the capsules follows the pattern of those of Phlebodium (Wilson, 1958a), Xiphopteris and Pyrrosia (Wilson, 1958b), and Anarthropteris (Wilson, 1960). Edwards (1996) expanded the examination of the structure of mature sporangia by initiating a survey of the cellular structure of the capsules of more than 110 species in 20 families. Three of these species were illustrated in his published abstract. Sporangia with four-rowed stalks, however, are known in several fern genera including Dipteris, Cheiropleuria, and members of the Cyatheaceae. Wilson (1959) pointed out that it was not possible to homologize the sporangial faces of Dipteris and Cheiropleuria with those of the higher leptosporangiate ferns. The known developmental patterns cannot give rise to a four-rowed stalk. Bower (1915) wrote that in Cheiropleuria sporangia with four-rowed stalks, the segmentation of the young sporangium, "Appears to show a regular cleavage of the segments in two opposite rows," and the "Subdivision of the two rows of segments of the stalk by walls in the plane of the drawings has given rise to the four rows of cells of the stalk, as seen in later stages." This suggests a distinctly different developmental pattern in these sporangia than is known. The only studies of the development of sporangia with four-rowed stalks are those of Bower (1915, 1923, 1926). Holttum and Sen (1961), in their paper "Morphology and classification of the tree ferns" did not make a detailed examination of the sporangia, but based their comments mostly on Bower's publications. For a clear understanding of the structure of the sporangia with fourrowed stalks their ontogeny needs to be studied in detail. Because it is readily available in cultivation in southern California, Sphaeropteris cooperi (F. Muell.) R.M. Tryon [Cyathea cooperi (F. Muell.) Domin] was chosen for study to serve as a model for the pattern of development of sporangia with four-rowed stalks. MATERIALS AND METHODS The material used in this study was collected from plants in cultivation in Los Angeles, California. A specimen of this fern has been deposited in the herbarium of Rancho Santa Ana Botanic Garden (Wilson 2067, RSA). Slides are deposited at Rancho Santa Ana Botanic Garden. Fertile pinnae of Sphaeropteris cooperi in early and increasingly mature stages of development were preserved in formalin-aceto alcohol (FAA). Sori were processed by three different methods: 1) Fertile pinnules were infiltrated with the tertiary butyl alcohol series, embedded in paraffin, and sectioned at 10,Lm. The sections were then stained in the Sharman (1943) series. 2) Fertile pinnules were cleared in 5% NaOH, bleached in 50% chlorine bleach, and stained in 3% tannic acid in 50% alcohol and 3% ferric chloride in 50% 205 This content downloaded from 207.46.13.149 on Wed, 28 Sep 2016 06:18:20 UTC All use subject to http://about.jstor.org/terms AMERICAN FERN JOURNAL: VOLUME 89 NUMBER 3 (1999) alcohol (the alcoholic stains were used to prevent maceration). After dehydration in alcohol, the sori were dissected from the pinnule lamina and placed on a slide in Diaphane. The sori were then teased to separate the sporangia and a coverslip was mounted. This technique resulted in an enormous amount of damage, but methodical searches of the slides and a large number of dissections revealed undamaged sporangia. This procedure of clearing and staining the sporangia allows both sides of each developing sporangium to be studied. 3) Young cleared fertile pinnules stained in tannic acid and ferric chloride were imbedded in paraffin, sectioned at 20pm, and mounted on slides. These preparations were studied to confirm the early division patterns observed in the other preparations. Mature sporangia were studied mounted in Crystal/Mount (Biomedia Corp., Foster City, California) on temporary slides. This process reduced the dehiscence of the capsules and at the same time prevented movement of the sporangia while being examined. All illustrations were made with the aid of a Leitz drawing tube on a Leitz microscope. Both sides of each cleared sporangium were drawn and each sporangial "Segment" is shaded to facilitate comprehension of the cell lineages in the developing sporangium. The shading patterns used conform with those used in earlier sporangial ontogenetic studies in order to allow for easier comparisons.