Morphology and wall ultrastructure of the spores of the Lower Devonian plant Oocampsa catheta Andrews et al., 1975

The enigmatic Lower Devonian plant Oocampsa catheta Andrews et al. (Can. J. Bot. 53 (1975) 1719) is considered intermediate between the trimerophytes and progymnosperms. In order to shed light on its evolutionary relationships, the morphology and ultrastructure of its sporangium and spores were analysed using light, scanning electron and transmission electron microscopy. In addition, dispersed spores (Grandispora douglastownense McGregor (Palaeontographica B 142 (1973) 1) and Grandispora ?macrotuberculata (Trudy VNIGNI 37 (1963) 18) McGregor (Palaeontographica B 142 (1973) 1), considered to possibly represent forms derived from O. catheta, were also examined. It is concluded that G. douglastownense and G. ?macrotuberculata are probably end members of the same spore complex and most likely are dispersed spores produced by O. catheta. Oocampsa catheta spores are bilayered. An inner body has an innermost part consisting of continuous, parallel-stacked, laminae and an outermost part consisting of more erratic, anastomosing, laminae. The inner body is surrounded by an homogeneous outer layer that is extended at the equator forming a pseudozona, and is folded on the proximal surface forming the trilete mark and on the distal surface forming spinose ornament. The spores are partially camerate. On the inside of the sporangium wall there is a layer probably representing the residue left following degeneration of a (probably secretory) tapetum. Spore morphology, gross structure and wall ultrastructure are compared to that of extant and fossil plant groups, and it is concluded that the spores of O. catheta are highly distinctive and do not conform closely to any plant group, although they show most in common with the spores of the progymnosperms.     

Permanent dyads in sporangia and spore masses from the Lower Devonian of the Welsh Borderland

Dyads, interpreted as cryptospore permanent dyads, are reported from sporangia and spore masses recovered from fluviatile deposits of Lochkovian (Early Devonian) age from the Welsh Borderland. The morphology, anatomy and ultrastructure of the specimens have been analysed using LM, SEM and TEM. Two specimens consist of a single sporangium terminating an axis: one is cup-shaped and attached to an unbranched axis and named Culullitheca richardsonii gen. et sp. nov., the other comprises an isotomously branching axis with one sporangium preserved and is named Fusitheca fanningiae gen. et sp. nov. Two specimens show dyads adhering to cuticular fragments presumably derived from sporangia. In one the cuticle is of irregular shape, in the other it is elliptical. The final specimen comprises an elongate spore mass. In all cases ultrastructural analysis reveals that the spore walls are essentially homogeneous. Our findings suggest that cryptospore permanent dyads were produced by rhyniophytoid plants of small stature. The affinities of these plants remain conjectural, as is the relationship of the cryptospore permanent dyads with other sporomorph morphotypes (cryptospores and trilete spores). However, the production of dyads by a plant with a bifurcating sporophytic axis is evidence against affinity with extant bryophytes. The mode of formation, adaptive significance, affinities, phylogenetic relationships and stratigraphical history (including demise) of cryptospore permanent dyads is discussed.     

Fossil plants with spores in the sporangia from the Upper Devonian (Frasnian) deposits of northern Timan

Fossil plants from the Upper Devonian (Frasnian) of northern Timan are studied. The sporangia contain well-preserved spores, which were studied in transmitted light using a scanning electron microscope. The genus Gutzeitia S. Snigirevsky, gen. nov. is established. Macroremains and in situ spores of G. timanica (Petros.) S. Snig., comb. nov. and ?Cephalopteris mirabilis (Nath.) Nath. are described. Microspores in Dimeripteris gracilis Schmalh. are identified, and microspores and megaspores in ?Cephalopteris mirabilis are studied for the first time.     

Early evolution of life cycles in embryophytes:A focus on the fossil evidence of gametophyte/sporophyte size and morphological complexity

Embryophytes (land plants) are distinguished from their green algal ancestors by diplobiontic life cycles,that is,alternation of multicellular gametophytic and sporophytic generations.The bryophyte sporophyte is small and matrotrophic on the dominant gametophyte; extant vascular plants have an independent,dominant sporophyte and a reduced gametophyte.The elaboration of the diplobiontic life cycle in embryophytes has been thoroughly discussed within the context of the Antithetic and the Homologous Theories.The Antithetic Theory proposes a green algal ancestor with a gametophyte-dominant haplobiontic life cycle.The Homologous Theory suggests a green algal ancestor with alternation of isomorphic generations.The shifts that led from haplobiontic to diplobiontic life cycles and from gametophytic to sporophytic dominance are most probably related with terrestrial habitats.Cladistic studies strongly support the Antithetic Theory in repeatedly identifying charophycean green algae as the closest relatives of land plants.In recent years,exceptionally well-preserved axial gametophytes have been described from the Rhynie chert (Lower Devonian,410 Ma),and the complete life cycle of several Rhynie chert plants has been reconstructed.All show an alternation of more or less isomorphic generations,which is currently accepted as the plesiomorphic condition among all early polysporangiophytes,including basal tracheophytes.Here we review the existing evidence for early embryophyte gametophytes.We also discuss some recently discovered plants preserved as compression fossils and interpreted as gametophytes.All the fossil evidence supports the Antithetic Theory and indicates that the gametophytic generation/sporophytic generation size and complexity ratios show a gradual decrease along the land plant phylogenetic tree.     

A probable pteridosperm from the uppermost Devonian near Ballyheigue, Go. Kerry, Ireland

A new genus of pleridosperms is described from the uppermost Devonian beds from Ballyheigue, Ireland. I.aceya hibernica May & Mat ten is represented by stems bearing spirally arranged fronds. The base of the frond is swollen and is about the same size as the stem. Pinnae are borne alternately and apparently in one plane on the rachis. The anatomy of the stem reveals a three-fluted protostele. Secondary xylem consists of rays and trachcids and secondary phloem is present. The inner cortex contains probable secretory and/or sclerotic cells. The outer cortex is of the spargaimm-type. Rachial trace formation is described. The U-shaped xylem strand of the rachis lacks secondary tissue. Pinnae traces are V- to C-shaped. A presumed adventitious root has a triarch protostele, a parenchymatous cortex and lacks a 'sparganum' outer zone. I.aceya is believed to be a member of the Lyginopleridaceae. The divisions of the sympodial protoxylem strand forming the rachial trace is compared among the Aneurophytales, Buteoxylonaceae, Calamopityaceae and Lyginopteridaceae and is shown to be similar.     

抱囊蕨属—四川早泥盆世一新属

本文描述了四川早泥盆世陆地植物的一个新属种——江油抱囊蕨(Amplectosporangiumjiangyouense)。植物体茎轴裸露,等或不等二歧式分枝多次,在其远端区密集的二歧式分枝构成了一个椭圆状或梨状轮廓的能育顶枝系。孢子囊椭圆形,具短柄,呈单列侧生于能育枝的内侧。根据新植物显示的形态特征,除与一些早期陆地维管植物作了比较外,还初步探讨了它与种子植物珠被演化间的关系。     

Amplectosporangium—A New Genus of Plant from the Lower Devonian of Sichuan,China

A new genus and species Amplectosporangium jiangyouense, is described from the Pingyipu Formation (Siegenian) of the Lower Devonian in Jiangyou district, Sichuan, China. The plant consists of naked dichotomizing erect axes with terminal fertile branch-systems. Sporangia are oval-shaped each with a short stalk and are arranged along the inner side of dichotomized axes in single row. By comparison with other known Devonian plants the genus is considered to represent a new morphological type of early land plants. Based on the theory of the telomic origin of the ovular integument, the plant may represent an early stage in the evolution of integument.     

猪苓分生孢子产生的电镜研究

The ultrastructure of conidia produced by the mycelia of Polyporus umbellatus was studied by use of scanning and transmission electron microscopy. The results suggested that only clamped (dikaryotic) mycelia produced aerial conidiophores with ovoid to rod-shaped conidia. There was a distinctive bulge near the top of the conidium. The contents of the conidia were dense. This type of conidium could be regarded as arthroconidia.     

A new Palaeozoic plant closely allied to Prototaxites Dawson

Three-dimensionally preserved coalified fragments recovered from upper Wenlock to Lower Devonian strata of the Welsh Borderland and South Wales are placed in a fourth genus of the Nematophytales Lang. It differs from Prototaxites only in its possession of internally differentially thickened tubes. The possible functions of the tubular and filamentous tissues are discussed in the context of the putative affinities and likely habitat (terrestrial or fresh water) of the new genus.     

Anatomical reinvestigation ofArchaeopteris macilenta from the Upper Devonian (Frasnian) of South China

Archaeopteris macilenta is one of the most widespread plants in the Late Devonian.Based on fossils from the Frasnian Huangjiadeng Formation,Yichang District of Hubei Province,for the first time we study in detail the anatomy of this progymnosperm plant in South China.Ultimate axes are protostelic with three xylem sympodia and lack secondary tissue.Penultimate axes are eustelic,bearing eight sympodia and a thin band of secondary xylem.Radially symmetrical sympodia of mesarch primary xylem produce traces of appendages in a spiral arrangement.Archaeopteris macilenta and A.halliana (A.roemeriana) are dominant in the Frasnian and Famennian,respectively.Comparisons with these two species from other tectonic plates indicate consistent stelar architectures.Global spread,continuous occurrence,and identical anatomy during the Late Devonian indicate that Archaeopteris survived the Frasnian-Famennian extinction event.In this time,endemic genera and cosmopolitan taxa,including Archaeopteris,suggest the palaeogeographic isolation of South China and certain associations with other plates.     

Ultrastructure of some Cambrian palynomorphs from the Bright Angel Shale, Arizona, USA

Palynomorphs with complex resistant walls have been recovered from several Cambrian deposits in the continental United States. Those recovered from the Bright Angel Shale of Arizona typically preserve both a primary wall, and an outer envelope (synoecosporal wall) that encloses multiple spore-like bodies within. At least three distinct types of primary walls, are recognized with the TEM: 1) a unilaminate wall with a smooth inner surface and a sculptured outer surface, 2) a wall of three unornamented laminae of very uniform thickness, and, 3) a thicker wall with multiple thin, lightly-staining layers embedded in a darker matrix. This third type of primary wall bears a strong resemblance to those of certain Lower Devonian hilate cryptospore monads from the Welsh Borderlands. No extant algae produce spores with walls as thick or as complex, suggesting that these Cambrian palynomorphs were the desiccation-resistant spores of cryptogams belonging to the charophyte–embryophyte lineage. Multilaminate spore walls, which are characteristic of some extant liverworts and Paleozoic cryptospores, may have evolved via the fusion of separate, multiple laminae. This appears to be the primitive plant sporoderm type, but it may have evolved asynchronously with respect to the evolution of the embryophytic development of the sporophyte in land plants.     

早泥盆世始叶蕨（新属）及叶子起源的讨论

本文报道了滇东南文山地区下泥盆统坡松冲组（西根阶）地层中一陆生植物新属,种－纤细始叶蕨（Eophyllophyton bellum gen.et sp.nov),植物体矮小,多次二叉分枝,远端枝二列互生长出次一级二叉分枝为主的末级枝,枝系起源叶顶生成侧生,多次分叉,缩合,扁化,蹼化并部分并合,生殖单位可下垂,由二枚顶端内卷的孢子叶组成,孢子囊圆至肾形,沿远,端加厚带开裂,成列侧生在孢子叶相对面的叶轴上,上述特征表明新植物远比同期的莱尼类,三枝蕨类和工蕨类复杂和进化,并显示出和工蕨类的某些亲缘关系,文内还探讨了枝系起源叶（大型叶）的发生和演化。     

Cuticles of Nematothallus: a further enigma

EDWARDS, D. & ROSE, V. 1984. Cuticles of Nematothallus: a further enigma. Cuticles of Nematothallus Lang scnsu Edwards are described from a Lower Devonian (Ditton) exposure on the M50 motorway (Hereford and Worcester, England). Some bear highly distinctive cuticular thickenings sometimes surrounding perforations. The affinities of the cuticles, and the development and possible functions of the perforations are considered.     

The development of Archaeopteris: new evolutionary characters from the structural analysis of an Early Famennian trunk from southeast Morocco

A 5 m long trunk of a young Archaeopteris/Callixylon erianum tree from the Late Devonian of Morocco shows new branching patterns for early lignophytes. This progymnosperm tree produces a helical pattern of traces that we infer belonged to reduced, short-lived, primary (apical) branches (type A) as well as two types of adventitious traces (types B and H). We infer that type-B traces supplied branches that initiate close to the site of attachment on the trunk of some, but not all type-A branches in an irregular but nonrandom pattern. Unlike ephemeral type-A branches, those of type B persist and become long-lived, potentially permanent units of the architecture of Archaeopteris trees. Type-H adventitious traces are also short-lived and occur singly or in serial groups, but differ from traces of either type A or B branches by lacking differentiation into a readily identifiable organ category. We interpret type-H traces as supplying latent primordia that could develop into either adventitious roots or shoots depending on extrinsic factors. Our new data suggest that Archaeopteris had a wide range of branch primordium amplitude. Type-B branches compare with axillary lateral branch buds of some Early Carboniferous spermatophytes (Calamopitys) and are a major developmental departure from the strictly apical, pseudomonopodial shoot branching of older aneurophyte progymnosperms. Type-H traces suggest that Archaeopteris trees had some potential for formation of adventitious roots or shoots in response to environmental factors, such as partial burial by overbank sedimentation. Collectively, these novel methods of tree branching may partly explain the extraordinary success and worldwide dominance of Archaeopteris forests on fluvially dominated, Late Devonian floodplains.