DIMENSIONAL CORRELATIONS IN DEVELOPING SELAGINELLA SPORANGIA

With length of sporangia as a developmental index, the growth relationships of sporangia during differentiation were studied in strobili of Selaginella bigelovii. The strobili usually contain two rows of megasporangia and two rows of microsporangia with a mega- opposite a microsporangium at each node. Prior to the sporocyte stage a sporangium in a megasporangiate row is larger and elongates more rapidly than a sporangium opposite it at the same node in a microsporangiate row. The number of sporogenous cells is similar in sporangia of the same length from both rows until cell multiplication ceases in sporangia of the megasporangiate row, while it continues in sporangia of the same size in the microsporangiate row. The observed growth differences between sporangia of the micro- and megasporangiate rows are interpreted as events in the differentiation of two sporangial types.     

A Mid Devonian seed-megaspore from East Greenland and the origin of the seed plants

A new species of late Mid Devonian seed-megaspore from East Greenland is described and named as Spermasporites allenii . The formerly monotypic genus Spermasporites is emended to accommodate this new species. Rare specimens of S. allenii , with near complete sporangial contents, occur together with specimens showing proximally adhering microspores. These demonstrate that S. allenii was contained within a sporangium exhibiting extreme anisospory, which is interpreted here as functionally bisexual. This is a key element in understanding its reproductive function. The megaspore was shed along with some attached microspores giving it potential for both cross- and self-fertilization. This confers the advantages of heterospory without recourse to separate micro- and megasporangia. This provides a more likely mechanism for seed plant origin than the archaeopteridalean sporangium reduction model. Ultrastructural study of the megaspore wall confirms the progymnosperm affinity of S. allenii . Comparable forms include the Frasnian Spermasporites devonicus and the Famennian seed-megaspores isolated from Archaeosperma arnoldii .     

POROSTROBUS NATHORSTII SP. NOV.: A NEW SPECIES OF LYCOPSID CONE FROM THE EARLY PENNSYLVANIAN OF ILLINOIS

Thirty-one specimens of a small megasporangiate lycopsid cone referable to the genus Porostrobus Nathorst and abundant associated dispersed megaspores have been collected from Early Pennsylvanian strata in the Allied Stone Company quarry, Milan, Illinois. Based on other elements in the flora, the deposit is considered to be part of the Morrowan Caseyville Formation and probably of Namurian age. This is the first reported occurrence of Porostrobus in North America and the cones are recognized as a new species, P. nathorstii. The environment of deposition indicates that the cones may have been transported from the parent plant prior to preservation. Cones are preserved as coalified compressions measuring 15–36 mm long by 2.5–7 mm wide, and are characterized by an apical tuft of leaves up to 20 mm long. Sporophylls are spirally arranged on a narrow cone axis, lack a heel or keel, and have a long distal lamina. Sporangia contain a single functional megaspore tetrad. Mature megaspores are 750–1, 150 μm in diameter, have prominent trilete sutures raised to form a gula, and have numerous branched hairs confined to an equatorial band. Megaspores correspond to the dispersed form Setosisporites praetextus (Zerndt) Potonie and Kremp. Porostrobus nathorstii is the only species of the genus described to date that is monosporangiate.     

INVESTIGATIONS OF NORTH AMERICAN CYCADEOIDS: CONES OF CYCADEOIDEA

Delevoeyas , Theodore . (Yale U., New Haven, Conn.) Investigations of North American cycadeoids: cones of Cycadeoidea . Amer. Jour. Bot. 50(1): 45–52. Illus. 1963.—A reinvestigation of the morphology of cones of Cycadeoidea indicates that they did not expand into flower-like structures at maturity The microsporangiate region was actually a compound synangium fused peripherally and, for at least part of the time, along the inner surface surrounding the ovulate receptacle. Capping the microsporangiate region is a massive parenchymatous dome. Synangia were borne along trabecular structures which connected the outer part of the microsporangiate structure to the inner face. Pollen may have been released after an abscission of the entire compound synangium.     

PALEOZOIC LYCOPSID FRUCTIFICATIONS. III. CONSPECIFICITY OF BRITISH AND NORTH AMERICAN LEPIDOSTROBUS PETRIFACTIONS

A study was made of 30 apparently similar microsporangiate cone specimens of the lycopsid fructification Lepidostrobus found in coal balls of Middle Pennsylvanian age from Illinois and Kansas. None of these specimens was a complete cone, but at least 19 were large enough and well enough preserved to provide information regarding variation both within one cone and among several specimens. The data obtained substantiated the original assumption that all 30 specimens represented one species. Attempts to equate this one species with any of the similar, previously described North American taxa, Lepidostrobus coulteri, L. pulvinatus and Lepidocarpon magnificum-microsporangiate form, and the British taxon Lepidostrobus oldhamius, including the forms (α), (β), (γ) and pilosus, revealed that no significant differences existed among any of these taxa. Furthermore, all characteristics described for these taxa were referable to, and well within the range of variation of, the one species here analyzed. Differences among the taxa were found to represent only differences in maturation or normal variation. All these taxa are, therefore, conspecific and are assigned to one species which by priority is named Lepidostrobus oldhamius. The common association of the megasporangiate Lepidocarpon lomaxi with all these miorosporangiate cones, now recognized as representing the single taxon Lepidostrobus oldhamius, is strong evidence for the probability that Lepidocarpon lomaxi and Lepidostrobus oldhamius were produced by the same parent plant species.     

The role of Hydropteris pinnata gen. et sp. nov. in reconstructing the cladistics of heterosporous ferns

Large segments of intact plants that represent a heterosporous fern have been discovered within an aquatic plant community from the Late Cretaceous St. Mary River Formation near Cardston in southern Alberta, Canada. Branching rhizomes of Hydropteris pinnata gen. et sp. nov. are 1–2 mm wide. They produce fronds at intervals of 2–12 mm and bear numerous elongated roots. Fronds, up to approximately 6 cm long, are pinnate with subopposite to alternate pinnae that exhibit anastomosing venation. Large, multisoral sporocarps occur at the junctures of the rhizome and frond rachides. Both microsporangiate massulae and megaspore complexes occur within each sporocarp. Megaspore complexes are assignable to the sporae dispersae genus Parazolla Hall. Microspores are trilete, smooth-walled, and are embedded in episporal material of the massulae. A numerical cladistic analysis indicates that the heterosporous aquatic ferns are monophyletic, and not as closely related to either schizaeaceous or hymenophyllaceous ferns as they are to some other filicaleans. Systematic revisions are proposed to reflect newly recognized cladistic relationships within the heterosporous clade, and character originations in the evolution of heterosporous aquatic ferns are evaluated. Hydropteridaceae fam. nov. is proposed, and included with Salviniaceae and Azollaceae in the Hydropteridineae subord. nov., and the Hydropteridales Willdenow.     

Anatomical Structures of Microsporangiate Cone of Lepidodendrales-- Lepidos trobus Shanxiense sp. nov.

A new anatomically-preserved microsporangiate cone in the coal balls of Coal Seam No. 7 (P1′) at the upper part of Taiyuan Formation in Xishan Coal-Field, Taiyuan, Shanxi Province of China was described. Having been studied, it was placed into Lepidostrobus Brongniart and considered as a new species. Vegetative organs of Lepidodendrales from mainly belonged to the natural genus Lepidodendron, such as stems, leaves and roots in the coal balls were visualized. However a few of them probably belonged to the natural genus Sigillaria. Besides, the single megasporophylls with megasporangia of Achlarnydocarpon (the megasporangiate cone of Lep/dodendron) have been found in the coal balls, so the specimens under discussion might belong to Lepidodendron. Lepidostrobus shanxiense sp. nov. The cone more than 3.5 cm long and 1.6～ 1.8 cm in width. The axis possesses siphonostele. The sporophylls on the axis in spiral arrangement. The pedicel 6～ 7 mm long and the distal lamina more than 1.2 cm long. The pedicel alate with alations extending about 2 ～ 2. 5 mm outward. The microsporangium probably bag-shaped, equal to the pedicel in length, 4.5 mm wide and 2～ 3 mm high, attached to the pedicel for about 2/3 of its length. The wall one cell thick in fully matured microsporan gia and consists of uniform columnar cells. The microspore 68～77μm in diameter, trilete and the surface minutely granular.     

ON THE STRUCTURE OF CALAMOSTACHYS BINNEYANA FROM THE LOWER PENNSYLVANIAN OF NORTH AMERICA

The discovery of specimens of Calamostachys binneyana in Lower Pennsylvanan petrifaction material in North America has provided additional information about the structure of this calamitean fructification. The cones consist of regularly spaced alternating whorls of bracts and sporangiophores. Bracts are fused in a disc except at the margin where the individual units become free. Sporangiophores are inserted at right angles to the cone axis and bear four axially directed sporangia. The vascular system of the North American specimens differs from that in other reports of the taxon in the presence of twelve vascular bundles in the cone axis. Each sporangiophore is supplied by a single vascular trace that departs from one axial bundle. There appears to be no constant relationship between the number of vascular bundles and the number of bracts. Spores are spherical, thin-walled, and of the Calamospora type. Relationships with other structurally preserved members in the genus are discussed in light of the diversity in structure demonstrated by the new specimens.     

Re-study of Minostrobus chaohuensis Wang (Lycopsida) from the Upper Devonian of Anhui,South China

Minostrobus chaohuensis Wang was previously known only as a lycopsid megasporangiate strobilus from the Upper Devonian of Anhui Province, South China. Our comprehensive study of the newly collected materials reveals the details of its morphology, anatomy, and reproduction, which allow us to emend its generic and specific diagnoses. M. chaohuensis is reconstructed as a plant with multi-dichotomous branching system, helically arranged leaves, and monoecious and monosporangiate strobili (i.e., separate megasporangiate and microsporangiate strobili in one individual). The anatomy of both fertile and sterile portions of Minostrobus indicates that the exarch primary xylem strand is the solid protostele, with the peripheral protoxylem ridges and Williamson's striations in metaxylem tracheids. The key reproductive and anatomical characters suggest that Minostrobus chaohuensis is far more likely to represent a distal shoot of pseudo-herbaceous or arborescent lycopsids within the order Isoëtales sensu lato. It is suggested that the monosporangiate-strobilus clade in the Isoëtales may include primitive, monoecious taxa in the Late Devonian and advanced, dioecious ones in the Carboniferous. The hypothesis that the more phylogenetically advanced monosporangiate-strobilus clade might have well diverged from the basal bisporangiate-strobilus clade of arborescent lycopsids by the Late Devonian is further supported.     

Histology of sterile male and female cones in<Emphasis Type="Italic"> Pinus monticola</Emphasis> (western white pine)

Two years of histological samples were collected from a Pinus monticola Dougl. (western white pine) tree identified as not producing mature pollen or seed cones. Anatomical information was collected to the ultrastructural level, to assess possible mechanisms for pollen and cone abortion resulting in sterility. Development of male and female gametophytes in the sterile western white pine tree was arrested after meiosis and before further cell divisions could take place. Sterile male gametophytes (pollen grains) had poorly developed pollen walls and sacci, reduced and degenerative cytoplasm, and no evidence of stored starch grains. The pollen cone aborted prior to pollen dehiscence. Meiosis of the megaspore mother cell in the ovule produced four megaspores, but development was stopped at the functional megaspore stage. The seed cone aborted in the first year of growth before winter dormancy. Tapetal tissue in sterile microsporangia appeared similar to that of fertile microsporangia, until the vacuolate, uninucleate microspore stage. Tapetal cells and thecal fluid surrounding the sterile microspores persisted well past the time when microsporangia on fertile trees started the process of maturation and desiccation. At pollen dehiscence, sterile pollen cones did not release any pollen and the microsporangia were filled with a sticky fluid. The behaviour of the tapetum in P. monticola sterile cones is compared with reports of tapetal function and malfunction reported in studies of angiosperm and other gymnosperm species. The occurrence and timing of gametophyte abortion in both cone sexes suggests a genetic rather than environmental basis for the sterility mechanism.     

Frenelopsis alata and its microsporangiate and ovuliferous reproductive structures from the Cenomanian of Bohemia (Czech Republic, Central Europe)

The conifer, Frenelopsis alata (K. Feistmantel) E. Knobloch (Cheirolepidiaceae), occurring mostly in the Cenomanian of Europe, is revised on the basis of the type material. Its comparison with relevant species of Frenelopsis is discussed.The ovuliferous cone associated with the genus Frenelopsis is recorded for the first time. For the associated ovuliferous cones of Frenelopsis, a new genus, Alvinia, is introduced in a new combination for the type: Alvinia bohemica (Velenovsky) comb. n. Its association with Frenelopsis alata is based on the presence of Classopollis pollen adhering to ovuliferous cone scales, and the same type of pollen found in the microsporangiate cone of F. alata, the same cuticle pattern present on ovuliferous cones, sterile twigs and microsporangiate cones of F. alata, and also the co-occurrence of ovuliferous cones or their scales and sterile twigs of F. alata.Large ovuliferous cones of Alvinia bohemica are formed by helically arranged ovuliferous scales subtended by bracts. Each ovuliferous cone scale displays one or two seeds covered by a covering flap, and three appendages, which form distally a funnel-like structure lined in its inner part by long trichomes. Numerous pollen grains of Classopollis adhere to the trichomes, and the structure is considered to function as a protostigmatic area.The ovuliferous cones of Alvinia differ from similar cones of the Cheirolepidiaceae, Hirmeriella and Tomaxellia, mainly in a high state of unification of the ovuliferous cone scale, reduction of appendages and in a presence of the protostigmatic funnel-like structure.The ovuliferous cones, Alvinia bohemica, rarely occur intact, so it is assumed that they disintegrate when mature. It seems likely that they were not woody. This assumption is supported by the flattened appearance of cones and their cone scales in the sediment, their flexibility and the absence of massive coaly matter known from cones of the Taxodiaceae and Cupressaceae. It is proposed that this type of ovuliferous cone scale indicates a specialized type of pollination. In addition, it is suggested that cone scales enclosing seeds play an important role in propagation.     

ULTRASTRUCTURAL STUDIES OF IN SITU DEVONIAN SPORES: BARINOPHYTON CITRULLIFORME

Each sporangium in the Upper Devonian taxon Barinophyton citrulliforme contains both microspores and megaspores. Microspores range up to 50 μm in diam and possess a homogeneous sporoderm characterized by an outer separable layer. The sporoderm of the megaspores (up to 900 μm) is constructed of sporopollenin units that are loosely arranged in the outer portion of the wall, and that give the megaspore wall a spongy organization. Ultrastructural evidence suggests that the small spores were not abortive megaspores, but that both spore types were functional. The spores of this plant, as well as other Devonian spores that show less dramatic size differences, are suggested as demonstrating a phase in the evolution of heterospory where sex determination was established in spores within the same sporangium prior to the evolution of micro- and megasporangia.     

A re-examination of Lepidostrobus Brongniart

Lepidostrobus is a genus that was established by Brongniart for Palaeozoic lycopod cones. Since then the genus has been used for a variety of cones that have similar characters. There is now compelling evidence that the genus represents a heterogeneous group of monosporangiate and bisporangiate cone species and that it should be divided. Lepidostrobus is rediagnosed as a genus of microsporangiate cones. Ftemingites Carruthers is rediagnosed as a genus of those bisporangiate cones formerly included in Lepidostrobus.     

STUDIES ON FOSSIL AZOLLA: PRIMITIVE TYPES OF MEGASPORES AND MASSULAE FROM THE CRETACEOUS

Fossil Salviniaceae are described from the Claggett Shale and Judith River Formation, late Cretaceous (Campanian stage) of Montana. A new genus, Parazolla, from the Claggett Shale, has megaspores in which the swimming apparatus is composed of a number of elongate floats attached to the megaspore body and invested by coiled hairs. The floats separate at maturity. Massulae (bearing microspores) have simple hair-like glochidia, many of which are knobbed at their tips. Glochidia tend to resemble the perisporial hairs of the megaspore body. This resemblance provides fossil evidence of the homology of these two hair-like structures among living species of Azolla. In Azolla simplex from the Judith River Formation the megaspore has a single cap-like so-called columellate float. Massulae, which have anchor-shaped glochidia, are associated with these megaspores. A. simplex is the oldest species of Azolla and Parazolla the oldest member of the Salviniaceae so far found.     

THE ANATOMY AND THREE-DIMENSIONAL MORPHOLOGY OF ANNULARIA HOSKINSII SP. N.

Foliage attached to calamitean shoots is described from coal ball petrifactions of Middle and Late Pennsylvanian age. Leaves correspond to the compression-impression genus Annularia and thus represent the first attached members of this genus to be recognized as petrifactions. Individual leaves contain a single unbranched vascular bundle flanked by wide lateral laminar areas which occupy more than half the leaf cross sectional area. Stomata are confined to broad bands within concave furrows which parallel the vascular bundle on the abaxial leaf surface. Epidermal cells within these furrows are in rows aligned obliquely to the leaf axis, and the rows angle outward at a slight angle towards the leaf margin. Convolutions of the leaf-bearing axes result from nodal diaphragms which are oblique to the shoot axis. Whorled leaves apparently radiate outward in the plane of each obliquely positioned nodal diaphragm. This petrified material helps explain the apparent flattening of entire nodal diaphragms and leaf whorls within the same plane as seen in compression specimens. Annularia hoskinsii sp. n. is proposed, and the systematic position of structurally preserved Annularia foliage relative to the genus Dicalamophyllum is discussed.     

Reproductive Biology of Selaginella: I. Determination of Megasporangia by 2-Chloroethylphosphonic Acid, an Ethylene-releasing Compound

Control clumps of Selaginella wallacei Heiron., sprayed with distilled water with Tween 20, produced a high proportion of microsporangia. Similar clumps sprayed with 2-chlorethyl-phosphonic acid, and ethylene-releasing compound (Ethephon), at 7.65 and 76.5 mg/liter produced almost exclusively megasporangia. Treatment of Selaginella pallescens (Presl) Spring with Ethephon at 34 mg/liter caused the production of megasporangia in the microsporangiate files of the strobili. The possibility that ethylene may be involved in the regulation of heterospory in Selaginella is discussed.     

A new microsporangiate organ from the Lower Carboniferous of the Novgorod Region,Russia

A new species of the genus Telangiopsis, T. nonnae O. Orlova et Zavialova, was described on the basis of a microsporangiate organ from the Lower Carboniferous deposits of the Novgorod Region. The morphology of branching fertile axes, synangia, and sporangia was thoroughly studied. The three-dimensional system of fertile axes branches monopodially; ultimate axes bear numerous connivent bunches of synangia, which consist of three to six basally fused elongated ovate sporangia. The morphology and ultrastructure of prepollen grains were studied, which were extracted from the rock matrix surrounding the sporangia. The two-layered exine includes a well-developed endexine and an alveolate ectexine, with one-three rows of large thin-walled alveolae. The new species was compared with other Early Carboniferous microsporangiate organs.     

Ultrastructural interpretation of the Late Cretaceous megaspore Glomerisporites pupus and its associated microspores

The ultrastructure of the Late Cretaceous (Santonian–?early Campanian) megaspore Glomerisporites pupus and its associated microspores has been examined in an attempt to resolve a number of problems concerning the interpretation of their morphology. The new observations presented are based on an analysis of entire, fragmentary, and thin-sectioned specimens under scanning and transmission electron microscopes. These add to, and partly correct, previous observations on this taxon. They include the following: (1) The exine of the megaspore consists of thin, homogeneous, outer undulating and inner electron dense layers, with a thicker zone of spongy structure in-between. (2) The perispore (or perine) of the megaspore comprises four layers, in order towards the exterior: loose filamentous, dense filamentous, vacuolate, and columnar. (3) This is completely enclosed by a thick mat of hairs, which appears to be attached to the underlying perisporal layers by means of connections with a few of the “spines” that originate from the dense filamentous zone, and with some elements of the columnar perine. (4) The tripartite neck (acrolamella) of the spore, which is hidden beneath the mat of hairs, is predominantly an extension of the dense filamentous and vacuolate layers, but also involves the columnar layer, especially in the lower part. (5) Some of the numerous small floats that are embedded in the mat have hairs originating from them. (6) Both long tangled and circinate hairs surround the perispore of the microspores. (7) The exine of the microspore was at least partly attached to the perispore when the organ was viable. (8) It comprises four zones that vary in structure and electron density. These facts and comparisons made with other megaspores and their associated microspores confirm evolutionary links between G. pupus and several taxa included within the Salviniaceae (Azolla, Parazolla, Salvinia) and possible ancestors of this group (the parent plants of Ariadnaesporites and Capulisporites).     

MEGASPORE WALL ULTRASTRUCTURE IN ISOETES

In Selaginella, megaspore wall ultrastructure (unit morphology and arrangement) is correlated with taxonomic position. In some Pennsylvanian lycopods there is a correlation with dispersal strategy. This study was designed to assess any correlation between habitat preference and wall ultrastructure in Isoetes. Except for a few minor structural correlations, wall ultrastructure appears to be constant in terrestrial, amphibious, and aquatic species of Isoetes. Several distinct sizes of megaspores occur in some megasporangia and correspond to 1) full-size megaspores with siliceous coatings, 2) small megaspores with siliceous coatings, and 3) full-size megaspores without siliceous coatings. The uniformity in wall ultrastructure within modem Isoetes together with the lack of uniformity of fossil isoetalean megaspore wall ultrastructure suggest that the modem species of Isoetes are closely related.