THE COMPARATIVE MORPHOLOGY OF THE CANELLACEAE. IV. FLORAL MORPHOLOGY AND CONCLUSIONS

The morphology and anatomy of 105 flowers representing 13 species and 6 genera of the Canellaceae are summarized. The flowers are borne in axillary or terminal racemes, cymes, or small groups, or solitary, in an axillary or terminal position. The flowers are characterized as follows: bisexual, hypogynous; sepals 3, thick and leathery; petals, 5–12, free or united into tube at base, rather thick, in 1 or 2 whorls and/or spirals; androecium of 6–12 stamens united by their filaments forming a tube, anthers with longitudinal extrorse dehiscence; gynoecium of 2–6 carpels fused by their ventral margins; 2–6 placentae. There are 2 vascular bundles (rarely 3) to each sepal, 3 to each petal (some of the inner petals have only 1), 1 to each stamen and 1 trace to each carpel. The petal and stamen bundles have a common origin. All the data accumulated in this series on the Canellaceae indicate that the correct systematic placement of the Canellaceae is in the woody Ranales, perhaps in a complex with the Myristicaceae.     

THE TAXONOMIC SIGNIFICANCE OF THE HEAD-SCRATCHING METHODS OF BIRDS.

Birds scratch their heads in one only of two ways, either directly or indirectly, and one method is used by all members of the same family though not necessarily by all families in the same order. When related families have different head-scratching methods, then the behaviour can help in disentangling difficult relationships. Examples are given. In the case of the passerines, only the Timaliidae (babblers) scratch directly. The implications are briefly discussed; for example, on this evidence Picathartes is not a babbler. The Psittaciformes are a potentially rewarding group for future work.     

Gynoecium diversity and systematics of the Magnoliales and winteroids

Carpel and ovule structure was compared in representatives of all 11 families of the Magnoliales (Annonaceae, Canellaceae, Degeneriaceae, Eupomatiaccae, Himantandraceae, Magnoliaceae, Myristicaceae) and winteroids (Austrobaileyaceae, Illiciaceae, Sehisandraceae, Winteraceae). Special attention was paid to features that are constant at family level. Bisexual flowers are always protogynous. In all representatives studied the carpels are closed at anthesis. Caipel closure is attained in three different ways: (1) postgenital fusion of inner surfaces (Degeneriaceae, Eupomatiaccae. Winteraceae), or (2) occlusion by secretion (Austrobaileyaceae, Sehisandraceae), or (3) a combination of (1) and (2): in Annonaceae, Canellaceae, Myristicaceae there is a conspicuous secretory canal in the innermost part of the ventral slit; in Illiciaceae and Magnoliaceae there is a narrow canal in the innermost part of the ventral slit; and in Himantandraceae the ventral slit is postgenilally fused in the style but completely open in the ovary. In most families the carpels have a double stigmalic crest or they have two tips in the transversal symmetry plane (i.e. at right angles to the median plane). Stigmas are unicellular papillate in most families but the papillae are bi-to multicellular (uniseriate) in Degeneriaceae and Eupomatiaceae. An unusual cryptic exlracarpellary compitum was found in Himantandraceae and Sehisandraceae. Intrusive oil cells were found in the carpel epidermis of Illiciaceae and Sehisandraceae. Mature ovules vary in length between 0.15 and 1.1 mm. The outer integument is fully annular (not semiannular) in Degeneriaceae, Himantandraceae, Canellaceae, Myristicaceae, and Illiciaceae. A rudimentary aril occurs in Canellaceae, and originates at the same site as in arillate Annonaceae and Myristicaceae. The results most strongly support an Annonaceae-Myristicaceae-Canellaceae alliance, to some degree also an Eupomatiaccac-Degeneriaceae-Himantandraceae-Magnoliaceae alliance, and an Illiciaceae-Schisandraceae-Winteraccae-Austrobaileyaceae alliance.     

COMPARATIVE MORPHOLOGY AND PHYLOGENY OF THE RANALES

Comparative morphological studies of woody Ranales have established the primitive status of the group and hence their key place in angiosperm phylogeny. Significant advances in our knowledge of some ranalian families have been made in recent years. An attempt is made in the present review to bring together a range of morphological data (vegetative and floral anatomy, palynology and embryology) on the Ranales (sensu lato), with particular reference to research work published after the publication of Eames's (1961) book, and to discuss the relationships of the families. Recent ontogenetic studies have shown that the carpel of Drimys is ascidial and not conduplicate as earlier suggested. The inclusion of Degeneria in the Winteraceae is not supported by morphological data. Melville's gonophyll theory has been shown to be inapplicable to the magnoliaceous flower. The pollen of Schisandra is interpreted as derived and specialized rather than primitive as previously supposed. The removal of Schisandra from Magnoliaceae is upheld by morphological evidence. Recent morphological studies do not support a close relationship between Schisandraceae and Illiciaceae suggested by earlier authors. The Canellaceae shows similarities to Winteraceae, Magnoliaceae, Illiciaceae, Eupteleaceae and Myristicaceae. Transitional types of division of pollen mother cells found in Winteraceae, Schisandraceae and Annonaceae and their probable phylogenetic significance have been discussed. The Annonaceae, Winteraceae, Degeneriaceae, Magnoliaceae, Schisandraceae and Cercidiphyllaceae share several embryological features in addition to similarities in floral structure. Ruminate endosperm is regarded either as an archaic feature retained in some taxa or as a later and parallel development in others. Thus its value in assessing relationships seems to be doubtful. Myristicaceae has been shown to be closely related neither to the the Annonaceae nor to the Lauraceae. The suggested relationship of Eupomatiaceae to Annonaceae is not supported by palynology. Floral cortical vascular systems in Magnoliaceae, Annonaceae, Calycanthaceae and Myristicaceae have been compared and it is concluded that they may be vestigial structures. A great deal of similarity has been found between Lauraceae and Calycanthaceae in wood, node, flower structure and embryology. Further floral anatomical evidence has been adduced to support the removal of Scyphostegia from Monimiaceae. The Hernandiaceae show similarities to some members of Monimiaceae while the Gyrocarpaceae resemble the Lauraceae, Gomortegaceae and certain other genera of Monimiaceae. Available evidence from wood and floral anatomy and embryology indicates close relationships among Lauraceae, Monimiaceae and Hernandiaceae. Vegetative and floral anatomical and embryological data seem to indicate a place for the Chloranthaceae in the ranalian complex. Recent anatomical studies in the Nymphaeaceae show that the floral structure is of a primitive type with similarities to the woody Ranales. Available morphological evidence is considered inadequate to express an opinion on the splitting of the family. Ceratophyllaceae is regarded as a highly reduced ranalian family derived most probably from a nymphaeaceous stock. The gynoecium in Berberidaceae is interpreted as monocarpellate. No evidence has been found to support the tricarpellate view. Berberidaceae, Lardizabalaceae and Menispermaceae share several embryological features, while at the same time showing evidence of specialization, each in its own way. Thus they might have arisen from a common stock and early diverged along different lines. The occurrence of several types of embryo sac in Ranunculaceae may well be an indication of specialization, but their probable taxonomic value, if any, is not yet clear. The occurrence of numerous primitive features in Paeonia has been suggested as an argument for its retention in the Ranales. No evidence has been found to preclude the inclusion of Dilleniaceae in the Ranales. On the other hand, as opposed to similarities in wood and pollen characters between Dilleniaceae and Theaceae, floral anatomical and embryological features offer a sharp contrast between the two. The Ranales are believed to be polyphyletic. It has been tentatively suggested that two major phyletic lines may be recognized in each of the woody and herbaceous series: the magnolialian and lauralian lines in the former and the nymphaealian and berberidalian lines in the latter.     

COMPARATIVE STUDIES OF THE NODAL AND VASCULAR ANATOMY IN THE NEOTROPICAL CYATHEACEAE. III. NODAL AND PETIOLE PATTERNS; SUMMARY AND CONCLUSIONS

Comparative studies of the nodal and vascular anatomy in the Cyatheaceae are discussed as they relate to the taxonomy and phylogeny of the family. There is in the Cyatheaceae (excluding Metaxya and Lophosoria) a basic nodal pattern consisting of four major phases of leaf trace separations. Abaxial traces arise from the leaf gap margins, and the last abaxial traces from each side of the gap are larger and undergo numerous divisions. Distally adaxial traces separate from the gap margins, and the last adaxial traces are usually larger and undergo multiple divisions. In addition, medullary bundles frequently become petiole strands of the adaxial arc in the petiole. Rarely, cortical bundles form petiole strands in the abaxial arc in the petiole. Leaf gaps of the squamate genera of the Cyatheaceae are fusiform and possess prominent lateral constrictions which result from medullary bundle fusions and the separation of leaf traces. A characteristic petiole pattern is found in all members of the Cyatheaceae. There is an increase in the complexity of the petiole vascular tissue which results in a gradation from the undivided strand in Metaxya, to the three-parted petiole pattern in Lophosoria, and finally to the much-dissected petiole vascular tissue in the advanced genera. Nodal and vascular anatomy data basically support Tryon's phyletic scheme for the family. The Sphaeropteris-Alsophila-Nephelea line shows certain tendencies toward increased complexity of nodal and vascular anatomy, whereas the Trichipteris-Cyathea-Cnemidaria line shows the same anatomical and morphological characters in a direction of increased simplification or reduction.     

STUDIES IN THE EMBRYOLOGY OF COMPOSITAE. IV. THE TRIBE INULEAE

Embryology of Blumea malabarica, B. membranacea, Laggera pterodonta, Anaphalis busna and Vicoa auriculata has been studied. The anther is tetrasporangiate in all the members except in Blumea membranacea where it is bisporangiate. The anther tapetum is of the Periplasmodial type. Both tetrahedral and isobilateral pollen tetrads are found. Mature pollen grains are three-celled with thick spinous exine. The ovary is bicarpellary syncarpous and unilocular with a single basal ovule. In one instance in Blumea malabarica two ovules per ovary with a rudimentary septum separating them was observed. The single hypodermal archesporial cell functions directly as the megaspore mother cell. The embryo sac develops according to the Polygonum type. The synergids in Blumea malabarica are hooked while in other members they are pear shaped. There are three antipodal cells except in Blumea membranacea where they increase up to eight. Endosperm development in Blumea malabarica is of the Nuclear type while in Blumea membranacea and Laggera pterodonta it is of the Cellular type. One or two layers of endosperm persist up to maturity. Embryo development follows the Senecio variation of Asterad type. The embryological information of this tribe along with that of other tribes will be utilized in evaluating the interrelationships of the family Compositae in a later paper.     

十齿花属分类地位的研究

本文对过去认为与十齿花属近缘的科,属的形态,木材解剖,花粉形态等方面的特征进行了较全面的比较研究。结果支持最初作者置于卫矛科的意见,并建立十齿花亚科,置于卫矛亚科和雷公藤亚科之间。滇西北产者订为一所种。     

MORPHOLOGY, REPRODUCTION, AND THE 18S rRNA GENE SEQUENCE OF PIHIELLA LIAGORACIPHILA GEN. ET SP. NOV. (RHODOPHYTA), THE SO-CALLED 'MONOSPORANGIAL DISCS' ASSOCIATED WITH MEMBERS OF THE LIAGORACEAE (RHODOPHYTA), AND PROPOSAL OF THE PIHIELLALES ORD. NOV.

Pihiella liagoraciphila gen. et sp. nov. (Rhodophyta) is described for a minute endo/epiphyte that is commonly associated with members of the Liagoraceae ( Nemaliales, Rhodophyta). Algae are discoid or subspherical and grow to a maximum diameter of 400 μm. Attachment is via isolated elongate rhizoids that penetrate into the loosely filamentous structure of the host or by a pad of several coalesced rhizoids where the host has a more cohesive cortex. Elongate surface hairs are common. Gametophytes are dioecious, the spermatangia arising on surface cells, and carpogonia with elongate trichogynes borne directly on undifferentiated surface supporting cells. Large sporangia form on stalk cells across the upper surface of the plants, these appearing to be either monosporangial or the result of fertilization of the carpogonia and equivalent to undivided zygotosporangia. Carposporophytes and tetrasporangia are unknown. 18S rRNA gene sequence analyses indicate that Pihiella constitutes a clade of long branch length most closely related to the Ahnfeltiales. The unique morphology and reproduction of Pihiella , combined with a substantial genetic divergence from the Ahnfeltiales, suggest that it is sufficiently distinct to warrant placement in a new family and order. We therefore describe the family Pihiellaceae and the order Pihiellales to accommodate the new genus.     

FURTHER STUDIES OF PRESUMEDLY PRIMITIVE GREEN ALGAE,INCLUDING THE DESCRIPTION OF PEDINOPHYCEAE CLASS. NOV. AND RESULTOR GEN. NOV.1

The tiny jumping flagellate originally described as Pedinomonas mikron Throndsen was isolated into pure culture from Australian waters and its ultrastructure critically examined. Pedinomonas mikron differs in behavior and in features of the flagellar apparatus from P. minor, the type species from freshwater, and is referred to the new genus Resultor. The two genera are closely related and form the new class Pedinophyceae, which is characterized by features of the flagellar apparatus, mitosis, and cytokinesis. The flagella show the 11/5 orientation otherwise characteristic of Ulvophyceae and Pleurastrophyceae, but they are arranged end to end as in the Chlorophyceae. The flagellar root system is asymmetric and includes a rhizoplast that emerges from the base of one flagellum but subsequently associates with a microtubular root from the second basal body. Mitosis studied previously by Pickett-Heaps and Ott in Pedinomonas is closed, unlike in other green algae, and the spindle is persistent. No phycoplast or phragmoplast is formed during cytokinesis. The eyespot of the Pedinophyceae is located at the opposite end of the cell from the flagella and adjacent to the pyrenoid, as in the most primitive members of the Prasinophyceae. Members of the Pedinophyceae lack prasinoxanthin and Mg 2,4D, characteristic of certain other primitive green algae. The primitive green algae include the classes Prasinophyceae and Pedinophyceae. Micromonadophyceae Mattox et Stewart is considered a synonym of Prasinophyceae. Two new orders are established, Pedinomonadales, containing all known members of the Pedinophyceae, and Scourfieldiales, with the single family Scourfieldiaceae fam. nov. and the single genus Scourfieldia.     

COMPARATIVE MORPHOLOGY OF THE COCHLOSPERMACEAE. II. ANATOMY OF THE YOUNG VEGETATIVE SHOOT

The generic scope and systematic position of the Cochlospermaceae were evaluated using observations from the anatomy of the stem, node, and leaf. There are few basic differences in vegetative anatomy between Amoreuxia and Cochlospermum. Secretory cells and canals, dilated phloem rays, and banded phloem are unifying features. Mature nodal anatomy is 3-trace, trilacunar, and the leaves of both genera have elongate, unicellular, branched idioblasts in the spongy mesophyll. Bixa has some features in common with Amoreuxia and Cochlospermum but is distinctive in vascularization of the petiole, leaf anatomy, and vestiture. Rhopalocarpus is quite different from the above genera, and its placement in a separate family is justified on anatomical grounds. The Cochlospermaceae, consisting of Amoreuxia and Cochlospermum, seem more closely related to the Sterculiaceae and Tiliaceae than to the Flacourtiaceae, Cistaceae, or Violaceae.     

THE MORPHOLOGY, ULTRASTRUCTURE AND FUNCTION OF THE FEEDING APPARATUS OF SAYELLA FUSCA (C.B. ADAMS, 1839) (GASTROPODA: PYRAMIDELLIDAE)

Scanning and transmission electron microscopy in conjunctionwith histology and dissection were employed to investigate theforegut anatomy of Sayella fusca (C.B. Adams, 1839), a commonNew England pyramidellid snail. Certain aspects of the feedingapparatus of S. fusca, including the buccal pump and proboscisanatomy, depart from the characteristic pyramidellid plan. Somedifferences such as the position of the introvert/proboscisaperture and the common oral and stylet canal are shared withthe genera Turbonilla, Eulimella, and Pyramidella. Three characteristicsof the feeding apparatus are unique to S. fusca: (1) the buccalpump is not divided into two pouches but exists as a singlemuscular bulb; (2) the entire lumen of the buccal pump, notsimply a portion of it, possesses a cuticular lining; and (3)the salivary ducts never enter the muscular walls of the buccalpump. Histological studies of the salivary gland indicate thatthree types of secretory cells are intermittently distributedthroughout the entire gland rather than characterizing distinctregions as described for other members of the family Pyra-midellidae.In contrast to previous findings, the gland cells of S. fuscaexhibit a merocrine secretion. The taxonomic value of the buccalpump and proboscis morphology are discussed. ^*Present address: Dauphin Island Sea Lab, 101 Bienville Boulevard,Post Office Box 369–370, Dauphin Island, Alabama 36528USA. (Received 9 November 1993; accepted 1 October 1997)     

CARRAGEENANS FROM AUSTRALIAN REPRESENTATIVES OF THE FAMILY CYSTOCLONIACEAE (GIGARTINALES, RHODOPHYTA), WITH DESCRIPTION OF CALLIBLEPHARIS CELATOSPORA SP. NOV., AND TRANSFER OF AUSTROCLONIUM TO THE FAMILY ARESCHOUGIACEAE

Ten Australian representatives from seven of the 10 genera presently constituting the family Cystocloniaceae have been analyzed for their cell-wall galactans. Included in our survey are the monotypic Australian-endemic genera Austroclonium , Gloiophyllis , Erythronaema , and Stictosporum , one species of Craspedocarpus , three species of Rhodophyllis , and two species of Calliblepharis . As one of the species of the latter genus is endemic to Western Australia and presently undescribed, we illustrate its habit and anatomical features in formally proposing to name it Calliblepharis celatospora Kraft, sp. nov. All the species surveyed essentially produce typical iota (ι)-carrageenans, with the exception of Austroclonium . The sulfated galactans from Austroclonium predominantly contain the repeating units of ι-, alpha (α)-, and 6'-O-methylated ι- and α-carrageenans; whether these exist as discrete polysaccharides or a complex hybrid structure was not resolved. Thus, Austroclonium carrageenans resemble the polysaccharides from Rhabdonia , Areschougia , and Erythroclonium . Although these latter three genera are currently included in the large gigartinalean family Solieriaceae, all produce significantly different carrageenans from Solieria itself and related genera such as Eucheuma , Kappaphycus , Betaphycus , Sarcodiotheca , Agardhiella , Sarconema , and Callophycus . In consideration of these findings, as well as of significant anatomical similarities, we provisionally recommend reestablishment of the family Rhabdoniaceae Kylin (as the family Areschougiaceae J. Agardh) for Rhabdonia , Areschougia , Erythroclonium , and Austroclonium.     

TWO NEW MEMBERS OF THE BLASTOCLADIACEAE. I. TAXONOMY,WITH AN EVALUATION OF GENERA AND INTERRELATIONSHIPS IN THE FAMILY

Two new fungi in a small family of zoosporic phycomycetes, the Blastocladiaceae, are described. Both are included in the Brachyallomyces category, as sexuality has not been found in either one thus far. Microallomyces dendroideus from Costa Rica represents a new genus distinguished by its occurrence on animal or plant substrata rich in protein, its branched thallus in which pseudosepta are entirely lacking but growth is renewed by sympodially formed hyphal tips, and its small size. Allomyces reticulatus from California is the first species in this well-known genus to exhibit reticulately sculptured resistant sporangia. Its robust thallus is also unusual in that, despite the presence of the characteristic pseudosepta and branching with sympodially renewed hyphal tips, growth is ordinarily not unlimited as it is in all other species of the genus. The addition of these two new water molds to the Blastocladiaceae poses some basic questions regarding generic distinctions in the family. These problems are discussed and a working key to the genera is provided.     

OBSERVATIONS ON THE FINE STRUCTURE OF THE CRYPTOPHYCEAE. I. THE GENUS CRYPTOMONAS1,2

The fine structure of 3 members of the genus Cryptomonas, C. rostrella, C. reticulata, and C. calceiformis, has been examined. These species exhibit the features typical of the class Cryptophyceae. The presence of subpellicular trichocysts causes a regular folding of the periplast, and larger trichocysts are present within the gullet. The plastid contains thylacoids arranged in pairs and a prominent pyrenoid; both structures are enclosed in 4 membranes, the outermost of which is a rough endoplasmic reticulum. The nucleus, Golgi apparatus and the Corps de Maupas occupy characteristic positions within the cell, and are the most characteristic features. All these structures indicate that this algal class occupies a unique phylogenetic position.     

A NEW BASAL BALAENOPTERID WHALE FROM THE PLIOCENE OF NORTHERN ITALY

Abstract:  A new basal balaenopterid genus and species, Archaebalaenoptera castriarquati , is described and compared with all the living and fossil members of the family Balaenopteridae and related fossil rorqual-like taxa. It was found in the Lower Pliocene of northern Italy, and is characterized by a supraoccipital with a transversely compressed anterior process, the zygomatic process of the squamosal diverging from the longitudinal axis of the skull, very long nasal bones, and subtle exposition of the parietal on the dorsal wall of the skull. It is primitive in having a maxilla with a long ascending process that is posteriorly unexpanded and round, and a dentary that is straight and not bowed outward, unlike that of living Balaenopteridae. In particular, the discovery of this new genus suggests that, among the early members of Balaenopteridae, the acquisition of the typical sutural pattern shown by maxilla, frontal, parietal and supraoccipital preceded the acquisition of the feeding-related traits that are characteristic of the family. The primitive morphology of the feeding-related structures of A. castriarquati (i.e. the straight dentary and the flat glenoid fossa of the squamosal) suggests that this whale was unable to undertake the intermittent ram feeding typical of Balaenopteridae as efficiently as living members of the family.     

Stem anatomy of the dwarf subshrub Cressa cretica L. (Convolvulaceae)

Stem anatomy and development of medullary phloem are studied in the dwarf subshrub Cressa cretica L. (Convolvulaceae). The family Convolvulaceae is dominated by vines or woody climbers, which are characterized by the presence of successive cambia, medullary- and included phloem, internal cambium and presence of fibriform vessels. The main stems of the not winding C. cretica shows presence of medullary (internal) phloem, internal cambium and fibriform vessels, whereas successive cambia and included phloem are lacking. However, presence of fibriform vessels is an unique feature which so far has been reported only in climbing members of the family. Medullary phloem develops from peri-medullary cells after the initiation of secondary growth and completely occupies the pith region in fully grown mature plants. In young stems, the cortex is wide and formed of radial files of tightly packed small and large cells without intercellular air spaces. In thick stems, cortical cells become compressed due to the pressure developed by the radial expansion of secondary xylem, a feature actually common to halophytes. The stem diameter increases by the activity of a single ring of vascular cambium. The secondary xylem is composed of vessels (both wide and fibriform), fibres, axial parenchyma cells and uni-seriate rays. The secondary phloem consists of sieve elements, companion cells, axial and ray parenchyma cells. In consequence, Cressa shares anatomical characteristics of both climbing and non-climbing members. The structure of the secondary xylem is correlated with the habit and comparable with that of other climbing members of Convolvulaceae.     

AN INVESTIGATION OF THE PHYLOGENETIC AND ONTOGENETIC VARIABILITY OF SHOOT APICAL MERISTEMS IN THE CACTACEAE

The sizes, shapes and zonations of the shoot apical meristems of 22 species of cacti were examined. This family was chosen because of its great diversity of habits; the more primitive members are nonsucculent. leafy trees and more advanced members are highly specialized “leaf-less” stem-succulents. By combining these measurements with those already in the literature, a sample of almost 70 species was obtained. Apical meristems range in size from only 80 μm in diam in some species to as much as 1.500 μm in diam in others. The shape ranges from being flat to almost hemispherical. Despite the great range in size and shape of the apical meristems, or the range in the morphologies of the leaves and stems which are produced by the meristems. all apices had the usual zonation: tunica, central mother cells, peripheral zone, and pith-rib meristem. The sizes of each of the zones. expressed either as the number of cells per zone or expressed as a percentage of the whole apex. were highly variable. The variation in apical dimensions and zone sizes occurred both phylogenetically and ontogenetically. and this has been interpreted to indicate that the morphogenetic mechanisms which control apical size and zonation are easily modified, both during the development of individual plants and during the evolution of new species.     

ANATOMICALLY PRESERVED SEED CONES OF THE PINACEAE FROM THE EARLY CRETACEOUS OF VIRGINIA

A collection of anatomically preserved conifer cones from the Early Cretaceous of Virginia contains two new species of the extinct pinaceous genus Pityostrobus. Superficially, the fossil cones resemble those of modern species of Picea. However, the fossils reveal such a peculiar mixture of anatomical features that they cannot be assigned to any extant genus of the Pinaceae. One of the new species, Pityostrobus hueberi, is most comparable with Pityostrobus corneti Alvin from the Early Cretaceous of Belgium. Pityostrobus virginiana, the other new species, differs from all other members of the genus in only slight—but nonetheless significant—attributes. Pityostrobus hueberi and P. virginiana are the first species of this genus to be reported from Early Cretaceous sediments of the North American Atlantic Coastal Plain. As such, they increase our knowledge of the structural variation exhibited by ancient members of the Pinaceae.     

THE RHIZOMORPH APEX OF PAURODENDRON; IMPLICATIONS FOR HOMOLOGIES AMONG THE ROOTING ORGANS OF LYCOPSIDA

A rhizomorph of Paurodendron with an intact apex recently has been discovered in Upper Pennsylvanian sediments of Ohio, and this provides the anatomical evidence necessary to interpret structure, ontogeny and homologies among lycophyte rooting organs. The basal meristem of Paurodendron is radial and lenticular, and produces an apical plug of parenchymatous tissue similar to a root cap. The plug is surrounded by a furrow associated with radially aligned cells that demonstrate a developmental correspondence to the furrow(s) of Isoetes. Based on external structural similarities at the rhizomorph apices of Paurodendron, Stigmaria, and young Nathorstiana, and on the anatomical similarities of Paurodendron to Isoetes, Stigmaria, Chaloneria, and Lepidocarpon embryos, all are interpreted as having a rooting organ that represents a modified shoot system that is fundamentally unlike the primary root system of seed plants. Likewise, the rootlets of rhizomorphic lycophytes are interpreted as leaves modified for rooting, and that have the equivalent of exogenous origin. As such, they are fundamentally unlike the adventitious roots of rhizomatous lycophytes like Lycopodium and Selaginella.     

THE MORPHOLOGY OF STIGMARIA STELLATA

Stigmaria stellata Goeppert is a lycopod underground system occurring in Upper Mississippian and equivalent age rocks of Europe and North America. This taxon has previously been based on impressions exhibiting radiating ridges and furrows around each lateral appendage scar and numerous polyhedral projections on the remainder of the axis. Anatomically preserved specimens from the Chester Series (Upper Mississippian) of Illinois reveal that the distinctive surface pattern of this species results from polyhedral wedges of thick-walled cells in the outer cortex. Decortication produces a smooth outer surface that is indistinguishable from that of the much more abundant Stigmaria ficoides. The structure of S. stellata is quite similar to the structure of other petrified stigmarians, but the following are some of the anatomical characters that distinguish it: (1) presence of abundant polyhedral wedges of thick-walled cells in the outer cortex; (2) absence of secondary cortex; (3) very tall rays associated with appendage traces that remain confluent with the secondary xylem to its outer margin; (4) the absence of a connective in the lateral appendages. The anatomical characters of Stigmaria stellata confirm it as a taxon of at least specific rank.