Palaeosmunda Emended and Two New Species

The genus Palaeosmunda was established by R. E. Gould in 1970 based upon some Late Permian Osmundaceous trunks with well-developed leaf gaps and rhomboidal sclerotic ring within petiolar base seen in cross section. As he thinks that the latter character is more important than the former, this genus could not be assigned to any subfamily of Osmundaceae. However, the leaf gap is one of the most important characters in the structure of the fern stem, so the author suggests that this genus should be assigned to subfamily Osmundoideae and its diagnosis must be emended as follows: The genus Palaeosmunda is represented by some rhizomes (or trunks), roots and leaf bases of ferns which structurally are preserved, resembling Osmundacaulis but which can’t be assigned to any group of this genus. Stem containing an ectophloic dictyoxylic siphonostele; if tracheids present in the pith, they being multiseriate scalariform pitted; pith or cortex sometimes contain ing groups of secretory cells or sclerenchyma; number of leaf traces seen in a tran sverse section of cortex more than 30; leaf traces adaxially curvature, rarely oblong shaped; petiolar bases with or without stipular expansion, containing a C-shaped vascular strand; root diarch. Type species——Palaeosmunda williamsii. According to this diagnosis some primitive osmundaceous species with the leaf gaps, which have already found in Upper Permian and Lower Triassic, could be assigned to this genus. Two of them are P. williamsii Gould and P. playfordii Gould, and Osmundacaulis beardmorensis, which was from Lower Triassic of Antarctica in 1978, should be assigned to the genus Palaeosmunda. In this paper two osmundaceous new species: P. primitiva and P. plenasioides were found in the coal balls of Upper Permian age from Wangjiazhai of Shuicheng of Guizhou Province, China. P. primitiva is represented by two trunks; stem about 4 cm in diameter; stele actophloic dictyoxylic siphonostele; pith cavity about 3—4 mm in diameter, contianing parenchyma and tracheids; xylem cylinder thin, less than 10 tracheids in radial thickness, dissected by leaf gaps. Inner cortex about 1.5 cm thick, mainly parenchymatous, but sometimes containing a few sclerenchymatous; number of leaf traces seen in a transverse section about 50—60; leaf traces departing at 35—45º,open C-shaped at point of departure, gradually becoming shallow C-shaped or V-shaped in different parts; protoxylem in base of leaf traces single, endarch; when leaf traces pass through inner cortex, protoxylem biturcating. Petiole bases without stipular expansion, probablyloosely embracing the stem; xylem strand of potiole trace shallow C-shaped, surrounded by selerenchyma; sclerotic ring round, connected with single sclerenchyma mass in the concavity of the petiole trace. Root arising singly from leaf trace, diarch, with inner and outer cortex. P. plenasioides is represented by a rhizome; stem more than 4 cm in diameter; stele actophloic dictyoxylic siphonostele; xylem cylider with about 20 tracheids in radial thickness, dissected by leaf gaps; xylem bundle U-, O-, or crosier- (i.e. query-) shaped; pith and inner cortex parenchymatous, with many groups of secretory cells; leaf trace C-shaped, its base containing two endarch protoxylem groups; root diareh,with inner and outer cortex, arising singly from leaf trace or its base.     

Anatomically preserved Woodwardia virginica (Blechnaceae) and a new filicalean fern from the middle Miocene Yakima Canyon flora of central Washington, USA

Anatomically preserved Woodwardia virginica (Blechnaceae) and a newly recognized onocleoid fern are described from the middle Miocene Yakima Canyon flora of central Washington State, USA. Identification of the W. virginica fossils is based on a combination of vegetative pinnules, rhizome and stipe anatomy, and fertile pinnules with indusiate sori and sporangia like those of extant W. virginica. Fronds are isomorphic. Vegetative pinnae are elongated and pinnatifid, with a secondary vein paralleling the midvein. Secondary veins of the pinnule lobe anastomose to form primary areoles and are either simple or dichotomize toward the margin. Rhizomes have a simple dictyostele with 3-5 cauline vascular bundles and often a sclerotic hypodermis. Leaf traces contain two large adaxial vascular bundles that occur laterally and adaxially, flanking an arc of 4-6 smaller bundles. Fertile pinnules have linear sori that are somewhat embedded in the laminae and are enclosed by a thin indusium. Leptosporangia display a vertical annulus and an elongated stalk. A second fern, Wessiea yakimaensis gen. et sp. nov., is represented by anatomically preserved branching rhizomes and attached frond bases that conform to the Onoclea-type pattern of rhizome and frond-base vasculature. Rhizomes have a simple dictyostele of 4-5 cauline meristeles. Leaf divergence is helical, with paired hippocampiform rachial traces. These two ferns occur in the same matrix with specimens of Osmunda wehrii. They demonstrate that filicalean fern assemblages similar to those of extant temperate floras were well established in western North America by the middle Miocene and further emphasize the exceptional species longevity of some homosporous pteridophytes.     

THE VEGETATIVE ANATOMY OF SCHOPFIASTRUM DECUSSATUM FROM THE MIDDLE PENNSYLVANIAN OF THE ILLINOIS BASIN

Schopfiastrum decussatum, a monostelic pteridosperm, has been recovered from Middle Pennsylvanian age coal balls from six localities within the Illinois Basin. Additional features of stem anatomy include the presence of horizontal sclerotic plates in the inner cortex, secretory ducts in the inner and outer cortex, and adventitious roots. The primary xylem is interpreted as bilobed, emitting massive leaf traces in a distichous manner. Five orders of frond members are described, including pinnules. All orders of the frond contain secretory ducts and tissues characteristic of Schopfiastrum stems. The rectangular, bilobed protostele, and method of leaf trace origin indicate that Schopfiastrum is more closely related to certain lower Carboniferous seed ferns than to contemporary Pennsylvanian pteridosperms.     

Osmunda (Osmundaceae) from the Triassic of Antarctica: an example of evolutionary stasis

Compressed specimens of the fern Osmunda are described from the Triassic of the Allan Hills, Antarctica. The specimens consist of a once pinnate, deeply pinnatifid fertile frond as well as several sterile specimens. Six pinnae are present on the partial fertile rachis, with two sterile pinnae above four fertile pinnae. Both sterile and fertile specimens are virtually identical to the modern species Osmunda claytoniana. Entire fronds are fragmentary; the longest is 21 cm in length. Sterile pinnae are alternate and deeply pinnatifid, with slightly toothed pinnules and dichotomous venation. Fertile pinnae are 1-1.3 cm long, once pinnate, and lack vegetative lamina. Sporangia are clustered, each 300-375 um in diameter, and possess a transverse annulus 6-8 cells long; dehiscence is by a vertical slit. Fronds arise from a rhizome 4 cm long by 1 cm wide; two croziers are present on the rhizome. Two frond segments up to 6 cm long and three deeply pinnatifid pinnae are present on the uppermost part of one rachis. Pinnules are ~4 mm long and 2-3 mm wide. The presence of this Osmunda species in the Triassic demonstrates stasis of frond morphology, both fertile and vegetative, for the genus.     

Size and reproduction of Thelypteris limbosperma and Athyrium distentifolium along environmental gradients in Western Norway

The performance of the ferns Thelypteris limbospgrma and Athyrium distentifolium , as expressed by number of son on pinnules and frond size, has been related to environmental gradients. Data have been collected from homogenous fern-dominated stands from different geographical areas in Western Norway. Number of sori produced, which was assumed to indicate fern fertility, was highly variable. There were significant correlations between frond size and fertility, but only 35–46 % of the variation in fertility could be explained by differences in frond size. The highest number of sori was found on plants of medium size, and for A. distentifolium there was a statistically significant reduction in sori number on fronds taller than 125 cm. For the linear relationships between fertility and size, it is suggested that the small X-intercept and slope defines the high competitive ability of A. distentifolium in sites with a long-lasting snow cover. The ferns may dominate in large stands even though their fertility is low or zero, which indicates that they under certain ecological conditions mainly reproduce vegetatively. Both ferns show decreased fertility both toward their altitudinal and lowland distribution limits, but their fertility optima were different. The performances of the two fern species showed highly different responses to geographical and climatical variables. The fertility of T. limbosperma could be predicted by mean July- and January temperatures, humidity and canopy cover, while the fertility of A. distentifolium could not be predicted by any of the site environmental variables investigated.     

STUDIES OF PALEOZOIC FERNS: THE FROND OF ANKYROPTERIS GLABRA

Eggert , Donald A. (Southern Illinois U., Carbondale.) Studies of Palerzoic ferns: The frond of Ankyropteris glabra. Amer. Jour. Bot. 50(4): 379–387. Illus. 1963—The major features of the frond of A. glabra are described on the basis of preserved parts found in Middle Pennsylvanian coal ball material from Illinois. The frond is planated and has well-developed foliar laminae. Primary pinnae arise from the petiole in 2 alternating series, and secondary pinnae arise in a similar fashion from the primary pinnae. Foliar laminae occur on the secondary pinnae and have dichotomous venation. The xylem of the petiole has a diupsilon configuration in the lower part of the axis, while higher in the petiole the xylem forms a strand resembling that of the European species A. westfaliensis. The xylem strands of the primary pinnae arise from the adaxial antennae of the petiolar vascular strand as somewhat C-shapcd bodies and develop antennae and become H-shaped at higher levels. A gap occurs in the antenna of the petiole vascular system above the level of departure of the primary pinna trace. Terete vascular strands occur in the secondary pinna axes which arise from the adaxial antennae of the xylem of the primary pinnae. The foliar laminae are relatively thin, have an irregular outline, and their histology is like that found in many living ferns. The frond of A. glabra illustrates that leaf evolution had progressed in at least one species of the coenopterid family Zygopteridaceae to the extent that an essentially 2-dimensional frond of modern aspect, and with well-developed foliar laminae, was present by Middle Pennsylvanian time.     

AUREALCAULIS CROSSII GEN. ET SP. NOV., AN ARBORESCENT,OSMUNDACEOUS TRUNK FROM THE FORT UNION FORMATION (PALEOCENE), WYOMING

Aurealcaulis crossii gen. et sp. nov., is based on permineralized trunks of an osmundaceous tree fern from the Paleocene Fort Union Formation from near Bitter Creek Station of southwestern Wyoming. This new species is characterized by centripetal (exarch) development of its xylem strands which form part of the leaf traces. Most of the leaf traces depart the stele as two segments that fuse into a single C-shaped petiole vascular strand outside of the outer cortex. Stipular expansions of the petiole bases of this species lack sclerenchyma, and roots arise from the lateral edges of leaf traces in the inner cortex. The family Osmundaceae and subfamily Osmundoideae are slightly emended to accept genera assignable to this family and subfamily with exarch protoxylem in their steles. Foliage similar to Osmunda greenlandica (Heer) Brown, which is possibly the leaf form of A. crossii, occurred next to an axis of this species which was in growth position. This axis was anchored in a lignite suggesting that this species grew under swampy conditions. Aurealcaulis crossii is the first arborescent member of the Osmundaceae of Tertiary age and the second arborescent form in this family reported from the Northern Hemisphere.     

A specialized new species of Ashicaulis (Osmundaceae,Filicales) from the Jurassic of Liaoning,NE China

A new species of structurally preserved fern rhizome, Ashicaulis plumites (Osmundaceae, Filicales), is described from the Middle Jurassic Tiaojishan Formation in western Liaoning Province, NE China. The new species is characterized by a peculiar sclerenchyma mass in the petiolar vascular bundle concavity. This sclerenchyma mass varies from a linear-shape to a mushroom-like shape with a remarkable outward protuberance, which distinguishes the present new species from other Ashicaulis species. Such a protuberance is very rare among osmundaceous ferns, and should represent a unique type for sclerenchymatous tissue in the osmundaceous vascular bundle concavity. Recognition of the peculiar structure of this new fossil species enriches anatomical diversity of permineralized osmundaceous ferns, indicating that the family Osmundaceae might have experienced a remarkable diversification during the Middle Jurassic in NE China. The new species show anatomical similarities to Osmunda pluma Miller from the Palaeocene of North America. The occurrence of A. plumites in the Middle Jurassic of China provides a new clue for understanding the evolution of some members of the living subgenus Osmunda.     

Todea from the Lower Cretaceous of western North America: implications for the phylogeny, systematics, and evolution of modern Osmundaceae

The first fossil evidence for the fern genus Todea has been recovered from the Lower Cretaceous of British Columbia, Canada, providing paleontological data to strengthen hypotheses regarding patterns of evolution and phylogeny within Osmundaceae. The fossil consists of a branching rhizome, adventitious roots, and leaf bases. The dictyoxylic stem has up to eight xylem bundles around a sclerenchymatous pith. Leaf traces diverge from cauline bundles in a typical osmundaceous pattern and leaf bases display a sheath of sclerenchyma around a C-shaped xylem trace with 2-8 protoxylem strands. Within the adaxial concavity of each leaf trace, a single sclerenchyma bundle becomes C-shaped as it enters the cortex. The sclerotic cortex is heterogeneous with an indistinct outer margin. The discovery of Todea tidwellii sp. nov. reveals that the genus Todea evolved by the Lower Cretaceous. A phylogenetic analysis combining morphological characters of living and extinct species with a previously published nucleotide sequence matrix confirms the taxonomic placement of T. tidwellii. Results also support the hypothesis that Osmunda s.l. represents a paraphyletic assemblage and that living species be segregated into two genera, Osmunda and Osmundastrum. Fossil evidence confirms that Osmundaceae originated in the Southern Hemisphere during the Permian, underwent rapid diversification, and species extended around the world during the Triassic. Crown group Osmundaceae originated by the Late Triassic, with living species appearing by the Late Cretaceous.     

Conantiopteris schuchmanii, gen. et sp. nov., and the Role of Fossils in Resolving the Phylogeny of Cyatheaceae s.l.

Conantiopteris schuchmanii gen. et sp. nov. The specimen, 23.2 cm long and 11.7 cm wide, shows helically arranged persistent frond bases embedded in adventitious roots, and is clothed by multicellular trichomes. A parenchymatous pith with mucilaginous cells and sclerotic nests is surrounded by an amphiphloic distyostele, parenchymatous inner cortex, and outer sclerenchymatous cortex. Sclerenchyma also surrounds the cauline vasculature and leaf traces. Medullary and cortical bundles are absent. Phloem contains both axially elongated and tangential sieve elements. Frond bases are oval in outline with three vascular bundles, including an undulating abaxial arc and an adaxial pair. Protoxylem of the stipe is endarch and is associated with cavity parenchyma. These characters are indicative of tree fern affinities. A cladistic analysis using trunk characters of both living and fossil tree ferns was conducted to help establish relationships of the new species and other fossil ferns, and to test hypotheses of general tree fern relationships. Additional analyses of living taxa only were also performed. Results from the analysis using both living and fossil taxa compare favorably with those that included only living species when either morphological characters or molecular sequences of the chloroplast gene rbcL are utilized. Although there are variations in the topologies of the various trees, results indicate that the new genus is nested among a paraphyletic assemblage of dicksoniaceous, lophosoriaceous, and metaxyaceous species that subtend a monophyletic Cyatheaceae s.s. Received 26 April 1999/ Accepted in revised form 15 July 1999     

The dynamic pipeline: hydraulic capacitance and xylem hydraulic safety in four tall conifer species

Recent work has suggested that plants differ in their relative reliance on structural avoidance of embolism versus maintenance of the xylem water column through dynamic traits such as capacitance, but we still know little about how and why species differ along this continuum. It is even less clear how or if different parts of a plant vary along this spectrum. Here we examined how traits such as hydraulic conductivity or conductance, xylem vulnerability curves, and capacitance differ in trunks, large‐ and small‐diameter branches, and foliated shoots of four species of co‐occurring conifers. We found striking similarities among species in most traits, but large differences among plant parts. Vulnerability to embolism was high in shoots, low in small‐ and large‐diameter branches, and high again in the trunks. Safety margins, defined as the pressure causing 50% loss of hydraulic conductivity or conductance minus the midday water potential, were large in small‐diameter branches, small in trunks and negative in shoots. Sapwood capacitance increased with stem diameter, and was correlated with stem vulnerability, wood density and latewood proportion. Capacitive release of water is a dynamic aspect of plant hydraulics that is integral to maintenance of long‐distance water transport.     

Structure-function constraints of tracheid-based xylem: a comparison of conifers and ferns

The ferns comprise one of the most ancient tracheophytic plant lineages, and occupy habitats ranging from tundra to deserts and the equatorial tropics. Like their nearest relatives the conifers, modern ferns possess tracheid-based xylem but the structure-function relationships of fern xylem are poorly understood. Here, we sampled the fronds (megaphylls) of 16 species across the fern phylogeny, and examined the relationships among hydraulic transport, drought-induced cavitation resistance, the xylem anatomy of the stipe, and the gas-exchange response of the pinnae. For comparison, the results are presented alongside a similar suite of conifer data. Fern xylem is as resistant to cavitation as conifer xylem, but exhibits none of the hydraulic or structural trade-offs associated with resistance to cavitation. On a conduit diameter basis, fern xylem can exhibit greater hydraulic efficiency than conifer and angiosperm xylem. In ferns, wide and long tracheids compensate in part for the lack of secondary xylem and allow ferns to exhibit transport rates on a par with those of conifers. We suspect that it is the arrangement of the primary xylem, in addition to the intrinsic traits of the conduits themselves, that may help explain the broad range of cavitation resistance in ferns.     

AN UNUSUAL BOTRYOPTERID SPORANGIAL AGGREGATION FROM THE MIDDLE PENNSYLVANIAN OF NORTH AMERICA

A new fertile species of Botryopteris (Botryopteridaceae: Filicales) is described from four incomplete Middle Pennsylvanian specimens. Fertile pinnae of B. cratis sp. n. consist of branched frond members bearing numerous globose sporangia. Surrounding the sporangial aggregations are larger sterile frond members (0.5-1.5 mm diam). Fertile pinnae are oval in transverse section and possess an eccentrically developed cortex composed chiefly of fibers. Some frond members show the typical botryopterid xylem configuration with three protoxylem strands. Spherical sporangia are loosely aggregated on the smallest pinnae by short, broad stalks. The annulus is band-like, two cells high, and extends transversely across the lower half of the sporangium for approximately half the circumference. Spores are oval, trilete, verrucate, and covered by a thin separable layer. Sporangium morphology is like that of Botryopteris antiqua, but the spores closely resemble those of B. globosa. The new species is unlike previously described fructifications of Botryopteris in exhibiting a small pinna system which surrounds smaller pinnae bearing sporangia in an aggregation. The new form is considered to be less specialized than previously described globosoid forms because the sporangia are much less crowded. Isolated frond members, believed to belong to the new species, have a large central arm in the pinna xylem trace that resembles the Stephanian taxon B. renaultii. Small stems attached to the adaxial surface of frond members are radial, protostelic, centrarch, and have a three-zoned cortex. The inner cortical zone contains large elongate cells with distinctive layered deposits. Stems are covered with uniseriate multicellular hairs on multicellular bases. Stems compare closely with B. mucilaginosa in histological features.     

FOSSIL OPHIOGLOSSALES IN THE PALEOCENE OF WESTERN NORTH AMERICA

Vegetative and fertile frond segments of Botrychium have been recovered from Paleocene deposits of central Alberta, Canada. Specimens are preserved as coalified compressions that yield information about frond structure, sporangia, and spore ultrastructure. These fossils, described as Botrychium wightonii sp. nov., establish a megafossil record for the Ophioglossales, and demonstrate that modern-appearing species of the order were present in western North America by the earliest Tertiary. The largest vegetative fragments are up to 4.6 cm long and tripinnately compound, with opposite to subopposite branching. Ultimate segments are pinnatifid with dentate pinnules and open dichotomous venation. Fertile specimens are also tripinnately compound with a long rachis and subopposite to alternate pinnae. Sporangia are either submarginal and superficial, or marginal, and are all directed toward one surface of the pinnule. They are ovoid to subspheroidal and 0.8-2.0 mm in diameter. Some sporangia are apparently stalked, while others appear to be sessile. This variation results both from the ultimate frond segments being compressed in several different planes, and the fossils being exposed at different levels. Spores macerated from the sporangia are radial and trilete, and range 30–67 μm in diameter. Most are psilate, but some have a densely striate surface.     

Reconstructing the Pennsylvanian-Age Filicalean Fern Botryopteris tridentata (Felix) Scott

Numerous anatomically preserved fragments of the Middle Pennsylvanian age filicalean fern, Botryopteris tridentata, occur in coal balls collected at the Pittsburgh and Midway Coal Company mine near Baxter Springs, Kansas. Included are the first fertile specimens of the species, evidence of complete vegetative frond architecture, and fronds that are specialized for vegetative propagation. Rhizomes are erect and unbranched, have helical phyllotaxis and short internodes, and typically display an ectophloic solenostele. Fronds are tripinnately compound with lobed pinnules that have open, dichotomous venation. Fertile pinnae or individual pinnules are interspersed among vegetative frond segments and produce sori of annulate sporangia beneath veins on the abaxial pinnule surface. Fertile pinnule lobes are rolled toward the abaxial surface to enclose the sori. Sporangia have a horizontally elongated biseriate annulus located near the short broad stalk and produce tetrahedral-shaped trilete spores with coarse spines. Epiphyllous branches diverge from the stipe or rachis, and some fronds produce only branches. This fern is reconstructed as having short stems. Helically arranged fronds are either pinnately dissected with lobed vegetative pinnules and abaxially rolled fertile pinnules or are specialized for vegetative propagation. The latter functioned as the foliar equivalent of stolons. While some characters of the B. tridentata plant are similar to those of Botryopteris forensis, generitype of the Botryopteridaceae, others are more comparable to those of Psalixochlaena cylindrica, generitype of Psalixochlaenaceae, suggesting the need for reevaluation of systematic relationships among species of the Botryopteridaceae and Psalixochlaenaceae.     

Paralygodium meckertii sp. nov. (Schizaeaceae) from the Upper Cretaceous (Coniacian) of Vancouver Island, British Columbia, Canada

More than 50 specimens of permineralized fertile pinnules with abaxially borne sporangia have been discovered in calcareous marine nodules from the Upper Cretaceous (Coniacian) Comox Formation from the Eden Main localities on Vancouver Island, British Columbia, Canada. Isolated pinnules 1.6–3.0 mm wide × 1.6–2.8 mm long are lobed and abaxially enrolled to form irregular globose structures. Pyriform sporangia 216–300 μm wide × 360–468 μm long occur in two rows on the abaxial surface of pinnule lobes. Sporangia have an apical annulus of 15–18 cells. Spores are tetrahedral and trilete, 33–42 μm in diameter, with straight to concave interradial sides, laesurae extending nearly to the equator, and a psilate exine. Spores are assignable to the sporae dispersae genus Deltoidospora. Fertile pinnules are compared to fossils of Anemia poolensis and two previously described species of Paralygodium, and show closest similarities to P. vancouverensis from the Eocene of British Columbia. The Cretaceous Eden Main specimens differ in number of pinnule lobes and their morphology and are described as a new taxon: P. meckertii sp. nov. This discovery extends the Cretaceous geographic range of Paralygodium from Japan to North America and adds to our knowledge of the diversity of extinct schizaeaceous ferns.     

Non-timber forest product harvesting in alien-dominated forests: effects of frond-harvest and rainfall on the demography of two native Hawaiian ferns

Non-timber forest products (NTFP) represent culturally and economically important resources for millions of people worldwide. Although many NTFP are harvested from disturbed habitats and therefore subject to multiple pressures, few quantitative studies have addressed this issue. Similarly few NTFP studies have assessed seasonal variation in demographic rates even though this can confound harvest effects. In Hawaiȁ8i, the wild-gathered ferns, Microlepia strigosa and Sphenomeris chinensis, represent highly important cultural resources but declining populations have led to conservation concerns. Both ferns are harvested from disturbed, alien-dominated forests and contemporary Hawaiian gathering practices often consist of harvest and concurrent weeding of alien invasive species. We assessed the effects of concurrent frond-harvest and alien species weeding on frond structure, density, and rates of production by comparing experimentally harvested vs. control plots, and documented relationships between frond demographic patterns and precipitation. Gathering practices had no impact on frond density of either species or on most other demographic parameters over the short term. Exceptions included a significant decrease in the density of the longest S. chinensis fronds and a significant decrease in M. strigosa frond production when fronds were gathered without alien weeding. However, seasonal and annual changes in frond density and production occurred across all plots of both species and were significantly correlated with precipitation. The relatively low harvest effects for both species are likely due to several factors including short frond longevity and the strict criteria used by gatherers to select harvestable fronds. The potential for sustainable harvest in the context of alien-dominated forests is discussed.     

The physiological implications of primary xylem organization in two ferns

Xylem structure and function are well described in woody plants, but the implications of xylem organization in less‐derived plants such as ferns are poorly understood. Here, two ferns with contrasting phenology and xylem organization were selected to investigate how xylem dysfunction affects hydraulic conductivity and stomatal conductance (g_s). The drought‐deciduous pioneer species, Pteridium aquilinum, exhibits fronds composed of 25 to 37 highly integrated vascular bundles with many connections, high g_s and moderate cavitation resistance (P₅₀ = ?2.23 MPa). By contrast, the evergreen Woodwardia fimbriata exhibits sectored fronds with 3 to 5 vascular bundles and infrequent connections, low g_s and high resistance to cavitation (P₅₀ = ?5.21 MPa). Xylem‐specific conductivity was significantly higher in P. aqulinium in part due to its wide, efficient conduits that supply its rapidly transpiring pinnae. These trade‐offs imply that the contrasting xylem organization of these ferns mirrors their divergent life history strategies. Greater hydraulic connectivity and g_s promote rapid seasonal growth, but come with the risk of increased vulnerability to cavitation in P. aquilinum, while the conservative xylem organization of W. fimbriata leads to slower growth but greater drought tolerance and frond longevity.     

Features of Egg Cells of Living Representatives of Ancient Families of Ferns

Examination of two species of osmundaceous ferns, two speciesof marattialean, and one dipterid, all representative of fernswith a long fossil history, has shown that the egg cells possessnumerous large amyloplasts. The nuclei of these egg cells alsoproduce no vesicular or sheet-like protrusions during maturation.In these respects the egg cells of the ferns examined differsharply from those of more recent ferns such as Pteridium andDryopteris. The significance of these findings is discussed. Egg cells, amyloplast, Macroglossum, Todea, Osmunda, Dipteris