Dichotomous Venation Research Articles

Studies on the Venation Pattern in Ferns I. Anastomoses and, other Features in <i>Adiantum incisum</i> forsk. (A. Caudatum Sensu Bedd., Non Linn. Pro Parte)

Anastomoses, though infrequent, occur in the dichotomous venation of Adiantum incisum Forsk. Generally more than one anastomosis does not occur in 2 single leaflet, but in three leaflets there were two anastomoses each. The anastomoses are classified into seven types. In Type I two branches of a single vein-dichotomy unite and the branches separate immediately after fusion. Type II anastomosis is similar to Type I but the branches do not separate after confluence. In Type III adjacent branches of two vein-dichotomies unite and separate after a short area of confluence. In Type IV two closely adjacent branches of two vein-dichotomies ale interconnected by a very short transverse commissural vein. Type V is similar to Type IV but the commissural vein is obliquely oriented. Type VI is characterized by the formation of an areole by the union of an unbranched arcuate vein and one of the branches of its sister vein lying above it. The region of confluence is very short and the branches again separate. Type VII is similar to Type VI but the branches do not divide after fusion. Vein approximations have been observed in addition to blind vein-endings, sinus vein-dichotomy, detached vein and marginal blind vein-dichotomy. It has been considered that the separation of Hewurdia to a distinct genus is unjustified. Certain phylogenetic aspects of vein-approximations and anastomoses are discussed.

Insight into the formation of trumpet and needle-type leaf in Ginkgo biloba L. mutant.

The leaf type of a plant determines its photosynthetic efficiency and adaptation to the environment. The normal leaves of modern Ginkgo biloba, which is known as a "living fossil" in gymnosperm, evolved from needle-like to fan-shaped with obvious dichotomous venation. However, a newly discovered Ginkgo variety "SongZhen" have different leaf types on a tree, including needle-, trumpet-, strip-, and deeply split fan-shaped leaves. In order to explore the mechanism in forming these leaf types, the microscopy of different leaf types and transcriptome analysis of apical buds of branches with normal or abnormal leaves were performed. We found that the normal leaf was in an intact and unfolded fan shape, and the abnormal leaf was basically split into two parts from the petiole, and each exhibited different extent of variation. The needle-type leaves were the extreme, having no obvious palisade and spongy tissues, and the phloem cells were scattered and surrounded by xylem cells, while the trumpet-type leaves with normal vascular bundles curled inward to form a loop from the abaxial to adaxial side. The other type of leaves had the characteristics among needle-type, trumpet-type, or normal leaves. The transcriptome analysis and quantitative PCR showed that the genes related to abaxial domain were highly expressed, while the adaxial domain promoting genes were decreasingly expressed in abnormal-type leaf (ANL) buds and abnormal leaves, which might lead to the obvious abaxialized leaves of "SongZhen." In addition, the low expression of genes related to leaf boundary development in ANL buds indicated that single- or double-needle (trumpet) leaves might also be due to the leaf tissue fusion. This study provides an insight into the mechanism of the development of the abnormal leaves in "SongZhen" and lays a foundation for investigating the molecular mechanism of the leaf development in gymnosperms.

Filmy Ferns (Hymenophyllaceae) and Associated Spike-Mosses (Selaginellaceae) from the Mid-Cretaceous Kachin Amber, Myanmar.

Filmy ferns (Hymenophyllaceae) are the most diverse lineage of the early-diverging leptosporangiate ferns with ca. 430 species widely distributed around the world but with the highest diversity in the humid tropics. However, their fossil record is scarce because of the low preservation potential of the delicate, membranous laminae. So far, no Hymenophyllaceae fossils have been reported from tropical Asia. Here, we describe some fern remains and their syninclusions (spike-mosses) in four pieces of Kachin amber from the mid-Cretaceous of Hukawng Valley, Northern Myanmar, as Hymenophyllites angustus sp. nov., H. kachinensis sp. nov., H. setosus sp. nov. (Hymenophyllaceae) and Selaginella alata sp. nov. (Selaginellaceae), respectively. These fern remains are assigned to Hymenophyllaceae based on the filmy, one-cell thick, decompound pinnatifid laminae and dichotomous venation. They represent the first fossil record of Hymenophyllaceae in tropical Asia. The growth habits of these ferns and associated spike-mosses and their implication for paleoenvironment are discussed. Our study expands the diversity of the cryptogams in mid-Cretaceous Kachin amber. Together with other contemporaneous findings, the present fossils indicate that Hymenophyllaceae have already accumulated some notable diversity in the Cretaceous.

New genus for megaphyllous leaves from the Upper Paleozoic of Mexico Velascoa pueblensis gen. nov

The paleoflora of the Matzitzi Formation has been studied since the beginning of the last century. Recent surveys have allowed the collection of abundant unregistered material, within which there is a notable group of leaves with a morphology similar to Ginkgophyta. The morphological analysis of more than 100 specimens resulted in the identification of large laminae with a long petiole, fan-shaped leaves with dichotomous venation and a characteristic constant segmentation that occurs up to three times and ends at the apex with 12 segments. It exhibits epidermal cells with sinuous to crenulated walls on the abaxial side, where anomocytic stomata and trichome bases can be observed. Given the absence of reproductive structures and the age of the material, its affinity to the order Ginkgoales is not possible; the comparisons were thus made with genera of the artificial group Ginkgophyta from different localities of the Upper Paleozoic. The results show significant morphological differences that support the proposal of a new genus and species, denominated Velascoa pueblensis. We also identified 10 orders and 27 genera that update the floristic lists created over 50 years ago. This information is important since it will allow to resolve future taxonomic, distributional, and/or environmental aspects that allowed the establishment of the taxa mentioned above.

Genome Sequencing of the Endangered Kingdonia uniflora (Circaeasteraceae, Ranunculales) Reveals Potential Mechanisms of Evolutionary Specialization.

SummaryKingdonia uniflora, an alpine herb, has an extremely narrow distribution and represents a model for studying evolutionary mechanisms of species that have adapted to undisturbed environments for evolutionarily long periods of time. We assembled a 1,004.7-Mb draft genome (encoding 43,301 genes) of K. uniflora and found significant overrepresentation in gene families associated with DNA repair, underrepresentation in gene families associated with stress response, and loss of most plastid ndh genes. During the evolutionary process, the overrepresentation of gene families involved in DNA repair could help asexual K. uniflora reduce the accumulation of deleterious mutations, while reducing genetic diversity, which is important in responding to environment fluctuations. The underrepresentation of gene families related to stress response and functional loss of ndh genes could be due to lack or loss of ability to respond to environmental changes caused by long-term adaptation to a relatively stable ecological environment.

London, When We

London, When We Katherine Robb (bio) When I broach the subject, my husband and I are tucked into the quilt of our home, a home that sits on a street lined with trees. One being the Ginkgo biloba, a living fossil with its dichotomous venation, its male and female trees separated, like people’s memories when they stand face-to-face and look over each other’s shoulders. Outside, giggling children run up and down the sloping sidewalks for which San Francisco is a mantra. “When, when, when,” he says. The girls I lived with in London, whom I don’t know anymore, whom I haven’t spoken with in years upon years, were my friends then. When we were young. When we lived in London. When we lived in London, we cooked everything in a pot someone swiped from the sidewalk. It was encased in rainwater next to a decrepit refrigerator whose door we couldn’t open until we could, which was immediately regrettable. When we lived in London, we memorized café menus like golden treasure maps until, through unanimous vote, the Pret A Manger egg-salad sandwich won best calorie-per-pound investment. We stole toilet paper from Starbucks when we lived in London. When we lived in London, all our possessions fit into one backpack. [End Page 143] Even then we knew we carried too much. When we lived in London, we hauled pots of boiling water down the stairs, steady, steady, don’t spill, pouring it swiftly into the calcified bathtub, splashing the two inches of warmth up over our curved bodies, over our youth. We submerged what we could of ourselves and waited, hunched at first, eventually placid, as the water cooled to tepid and then to cold, our lips and bellies and breasts all islands in the puddle. When we lived in London, the kitchen was sticky from toast slather remains, the jam congealing into a sweet strawberry lacquer and more than a few arguments. When we lived in London, we ate bangers at a street faire where someone bought patchwork pants and I threw up behind a stall. We weighed less and dreamed more when we lived in London. We drank Ribena at the house of a girl whose father made suits for the Beatles. We smiled when people asked if we were Canadian. When they realized we were American, we explained we didn’t understand why he was reelected either. When we lived in London, we still hadn’t decided who we wanted to be. Or so we told the others, and ourselves, sometimes. When we lived in London, a boy flew all the way from Cincinnati to ask a girl to marry him amidst the wafting Indian spices of our landlady’s cooking, and when the girl said no, when she said, “Go home,” and shut the door on his proffering, he flew back, across the sun. When we lived in London, I wore knee-high black leather boots with heavy buckles and four-inch lug platforms. Late at night, when we lived in London, we ate shawarma from carts after watching glitter-encrusted men prance on stages high above throbbing crowds. When we lived in London, we walked hard and fast down unlit streets, taking unsafe short cuts, whispering to ourselves: if they come at least they won’t have guns because this is London, this is not America, and here they have to look you in the eyes if they take you, which felt like something significant. We asked the boys, when we lived in London, the friends of the friends, how to take the absinthe with the sugar and the flames, how to take it in the Bohemian Method, because Bohemia, we thought, might be the answer, but we woke in the morning with black tongues and no hallucinations except the ones we brought with [End Page 144] us from across the pond. We were less magnetism, more bohrium when we lived in London. We didn’t know, when we lived in London, that absinthe, like so many other things, wasn’t what it used to be. When we lived in London, I invited someone, not you, for...

Senftenbergia oregonensis (Arnold) Comb. Nov. (Filicales): Delimiting Relationships among Paleozoic Tedeleaceae

Reexamination of fossilized plant material from the westernmost Pennsylvanian-age wetland flora in North America reveals that material of Pecopteris oregonensis Arnold represents a filicalean fern frond with annulate sporangia and anatomically preserved vascular tissues of the rachis. The frond, which is redescribed as Senftenbergia oregonensis (Arnold) Hillier et Rothwell comb. nov., is pinnately compound, with five orders of catadromous dissection, and it appears to have reached a length of 80 cm or more. The rachis displays an anchor-shaped xylem bundle, and dichotomizing aphlebiae are produced at the base of primary pinnae. The rachis, primary pinnae, and secondary pinnae have a dense covering of coarse trichomes. Secondary and tertiary pinnae display a length∶width ratio of 2.5∶1. The pecopterid pinnules measure 1.5–6 mm in length and 1.0–2.0 mm in width, with dichotomous venation, smooth-to-undulating margins, and a rounded tip. Sporangia are marginal and recurved under the abaxial pinnule surface t...

An Early Cretaceous zamiaceous cycad of South West Gondwana: Restrepophyllum nov. gen. from Patagonia, Argentina

The record of Cycadales in Patagonia begins in the Triassic and extends up to the Oligocene. In this region the group is highly diversified and includes several taxa represented by trunks, leaves and pollen cones. A new cycadalean genus and species, Restrepophyllum chiguoides, form the Aptian Anfiteatro de Ticó Formation, Santa Cruz province, Argentina, is described here. The fossil is a leaf compression with well-preserved cuticle. Its morphology, anatomy and ultrastructure are studied by means of light and electron microscopy. The leaf is lanceolate, serrate, and possesses a prominent midvein and decurrent laterals showing an open, simple or dichotomous venation. The leaf is hypostomatic, and the abaxial cuticle is thinner than the adaxial one. The stomata are irregularly distributed and indistinctly oriented between veins. They are monocyclic to imperfectly dicyclic (haplocheilic); the suprastomatal aperture is raised over the epidermis and the guard cells are sunken. Scattered trichomes and crystalliferous idioblasts are also present. The cuticle is composed of three layers: the outer and inner layers are lamellate, while the middle one is granulate. This new cycad leaf is compared with similar fossil leaves from Gondwana and Europe/North America, and also with similar extant cycad leaves. Based on the general morphology and the main characters of the cuticle, R. chiguoides is assigned to the family Zamiaceae; moreover it is more closely related to the living Zamia ( Chigua) restrepoi (D. Stevenson) Lindstrom than to any other member of the Cycadales. Paleophytogeographic evidence suggests a South American origin of Zamia/Chigua and a further migration to northern latitudes. This new type of leaf also suggests the putative existence of a Chigua clade that may be traced back to the Early Cretaceous when two cycadalean families, Zamiaceae and Stangeriaceae, were already well-established in Patagonia.

Kaplanopteridaceae fam. nov., Additional Diversity in the Initial Radiation of Filicalean Ferns

The Pennsylvanian filicalean fern Kaplanopteris clavata gen. et comb. nov. is reconstructed on the basis of permineralized vegetative and fertile frond segments and rhizomes. Characteristic anatomy conforming to morphospecies Anachoropteris clavata Graham allows for integration of new observations and reevaluation of materialfromOhiowithpublisheddataintothewhole-plantreconstruction.Epiphyllousrhizomesariselaterally alongfrondrachidesandfeaturetereteexarchprotosteles.Frondsareplanar,tripinnate-pinnatifid,withalternate division. Vascular traces of all frond members have adaxial, exarch protoxylem. Rachides and primary pinnae have adaxially convex C-shaped traces; secondary pinna traces are terete. Pinnules are laminar, with lobed margins and open dichotomous venation. Tripinnate latent croziers equivalent in complexity to whole fronds arise on otherwise mature frond segments at the position of primary pinnae. Superficial abaxial indusiate sori exhibit gradate maturation and include numerous leptosporangia producing trilete spores. Sporangial capsules arebentawayfromthecenterofthesorusatthejuncturewiththelong,uniseriatestalks.Theannulusisabandof twotothreerowsofinterfingeringcells,wrappedaroundthelongaxisofthesporangiumandcoveringmostofit. The longitudinal stomium faces toward the apex of the sorus. Kaplanopteris clavata is reconstructed as a primarily vining plant with organography overwhelmingly dominated by the frond and a unique life-history pattern influenced by growth from two types of foliar-borne reiterative units: latent croziers and rhizomes. Kaplanopteris combines characters known exclusively in fossil filicaleans with both plesiomorphic and derived characters of livingfilicaleans. This novel combination reveals the existence of a previously unrecognized lineage of basal filicaleans and justifies placement in a new family. Kaplanopteris illustrates the diversity and complexity reached during the first major evolutionary radiation of filicaleans.

New species of Rochipteris from the Upper Triassic of Australia

Two new species of the gymnospermous leaf form-genus Rochipteris Herbst, Troncoso and Gnaedinger are described. Leaves belonging to this genus are apetiolate, flabellate, with an entire to variably dissected apex, a truncate to slightly flaring base, and sparsely anastomosing venation. Rochipteris etheridgei (Arber) comb. nov. is documented from Carnian sediments of the Leigh Creek Coal Measures, South Australia. Rochipteris ginkgoides sp. nov. is described from the Ipswich Coal Measures (Carnian) Queensland, Australia. A single additional incomplete leaf from the Triassic Springfield Basin, South Australia is assigned to Rochipteris sp. These fossil leaves have previously been assigned to a range of genera based on leaf shape and apparent dichotomous venation. Rochipteris species represented a sub-dominant component of the Dicroidium-rich lowland vegetation across Gondwana during the Late Triassic.

Charbeckia macrophylla gen. et sp. nov. from the Lower Mississippian Price (Pocono) Formation of southeastern West Virginia

A fossil plant discovery from the Price (Pocono) Formation of southeastern West Virginia provides new information on the poorly known compression floras of the Lower Mississippian of North America. The new plant described herein consists of long tapering bipinnate fronds with imbricate basal pinnae, planate apical pinnae, and unlobed, elliptical to obovate pinnules with open dichotomous venation. Veins concentrated in the medial region of the pinnule curve toward the lateral margin, suggestive of an early stage in the evolution of a midrib. Pinnules exhibit a distinctly revolute or otherwise reinforced margin. The exceptional length of some fronds (over 1 m) and pinnule size (some over 3 cm by 2 cm) strongly contrast with the generally diffusely branched fronds and small or highly dissected pinnule morphology that typify Early Mississippian leaf taxa. A new generic assignment, Charbeckia macrophylla, is thereby justified. The rigid appearance of the tapering rachis, the imbricate pinnae that appear to have resisted compression, and the reinforced pinnule margins imply thick evergreen leaves, perhaps adapted for drought tolerance. A possible Calamopityalean affinity is indicated by the size of the fronds and the stout petioles, which fall within the expected size range of the Kalymma-type petiole bases described from the nearby New Albany Shale of Tournaisian age.

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.

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.

PALEOZOIC SEED FERNS: HETERANGIUM KENTUCKYENSIS SP. NOV., FROM THE UPPER CARBONIFEROUS OF NORTH AMERICA

Heterangium kentuckeyensis sp. nov. is described from Lower/Middle Pennsylvanian sediments of eastern Kentucky, based on permineralized stems, petioles, frond members, laminar foliage, and roots, including several organs in attachment. Stems 2.2 to 5.8 mm in diameter are known in several developmental stages. The considerable variability in stelar and cortical histology within this one species emphasizes the need to reassess variability within previously described taxa. Fronds of H. kentuckyensis are at least twice pinnate and bear primary pinnae alternately at approximately right angles. Laminar pinnules have dichotomous venation, are at least 2‐lobed, and comparable to foliage of the Sphenopteris‐type. Stomata possess 6–7 subsidiary cells with abaxial papillae. The characters used to distinguish the subgenera of Heterangium are evaluated and found to be unreliable. Moreover, suggested phylogenetic schemes both within Heterangium and between this taxon and other lyginopterid pteridosperms based on these features are inconsistent with stratigraphic data. Until reproductive features are known, the classification of Heterangium species is best based on characters of the vegetative sporophyte, including stelar organization (particularly protoxylem architecture), cortical histology, and frond morphology.

Diphyllopteris verticillata Srivastava, the probable seedling of Glossopteris from the Palaeozoic of India

Reinterpretation of Diphyllopteris verticillata Srivastava from the Lower Gondwana of India shows that in the seedling stage of Glossopteris, preserved vertically compressed in growth position. The first two seedling leaves are paired, costate, and have reticulate venation; they closely resemble adult leaves of Glossopteris except for their diminutive size. The two cotyledons borne at 90° to the seedling leaves, are opposite, dichotomously divided and have open dichotomous venation. Phylogenetic and palaeocological implications are discussed.

Developmental Morphology of Platycerium coronarium (Koenig) Desv

The growth habit and certain developmental aspects of Platycerium coronarium (stag's horn fern) are described. Starting from the primordial stage, the nest and pendulous leaves develop to maturity in 90 and 80 days respectively. The fertile lobe, which is part of the pendulous leaf, reaches its maximum size in 40 days. The morphogenesis of the nest leaf is more variable, and it matures and deteriorates earlier than the pendulous leaf. The acrostichoid sorus formation is completed in 3 weeks from inception and spore dispersal takes place when the fertile lobe is about 100 days old. The area of the fertile lobe and number of spores produced were determined. On Knop's agar medium the gametophytes develop in 2 months and 85 per cent of them are unisexual (both male and female) and 15 per cent bisexual. Less than 1 per cent of the gametophytes give rise to sporophytes. The juvenile leaves are simple, displaying open dichotomous venation; the first nest and pendulous leaves are produced 24 months after the date of spore germination.

Open dichotomous venation in the leaves ofUtricularia striatula (Lentibulariaceae)

The open dichotomous pattern of venation in the leaves ofUtricularia striatula is described in detail and compared withCircaeaster andKingdonia. Similar traits of dichotomous venation occur in other species ofUtricularia and may be due to reduction.

Fertile and sterile frond segments of the lyginopterid seed fern Feraxotheca

Fertile and sterile frond segments of the lyginopterid seed fern Feraxotheca culcitaus are described. In both the fertile and sterile specimen three orders of frond axes are borne alternately and in the same plane. Antepenultimate and penultimate frond axes are characterized by a C-shaped vascular bundle and numerous canals containing a golden-colored material in the fossilized condition. Synangia with only four sporangia demonstrate radial symmetry; bilateral symmetry is present in larger synangia. Pinnules possess dichotomous venation, with a single vein entering each lobe of the deeply incised lamina. A single canal occurs below each vein, and vein ends have an amplified vascular bundle. Morphologically Feraxotheca compares most closely with the compression genus Crossotheca. The morphology of the vascular bundle in the largest pinna is similar to a Lower Carboniferous specimen of Rhodea.

COMPARATIVE ONTOGENETIC STUDIES IN YOUNG SPOROPHYTES OF TREE FERNS. I. A PRIMITIVE AND AN ADVANCED TAXON

Ontogenetic studies of young sporophytes were undertaken to determine anatomical and morphological differences between a primitive (Lophosoria quadripinnata) and an advanced (Sphaeropteris elongata) tree fern. In both species the first leaf is simple, fanshaped, and possesses dichotomous venation. Later‐formed leaves exhibit either a pinnate or bipinnate pattern of laminar dissection. As the sporophyte matures, the stelar pattern changes from a protostele to an amphiphloic siphonostele, and finally to a dictyostele in Sphaeropteris. Medullation of the protostele occurs either prior to or after the formation of the first leaf trace in both species. Differentiation of xylem in the shoot is acropetal and the appearance of mature protoxylem occurs closer to the apical meristem in Sphaeropteris. The nodal pattern varies within each species with a no gap 1‐trace pattern characteristic for the first two or three leaves, depending upon the taxon. In Lophosoria subsequent leaves possess a unilacunar 1‐trace nodal pattern, whereas a complete nodal series (1 gap 1‐trace to 1 gap 6‐trace) occurs in Sphaeropteris. Fusiform leaf gaps are noted in both species. The shoot apical meristem is dominated by a single apical cell, with an organized apical cell first found in P2. Stem, root, and petiole anatomy are discussed.

ADDITIONAL STUDIES ON THE MORPHOLOGY OF BLIND VEIN‐ENDINGS IN THE LEAF OF CIRCAEASTER AGRESTIS

An intensive study has been made of the general structure and varied topography of blind vein‐endings in the dichotomous venation of Circaeaster agrestis Maxim. The venation patterns of leaves of plants collected in various parts of the geographical range of this species as well as the vasculature of leaves of specimens raised in a growth‐chamber have been studied and compared. Blind endings may be associated in various ways with the branches of simple terminal vein‐dichotomies and are either intrusive or extrusive in position. Descriptions are also given of the various relations between intrusive and extrusive blind endings and the more complex asymmetrical or symmetrical dichotomized vein‐systems found in various parts of the lamina. “Unlike the main veins of the leaf, which consistently vascularize corresponding marginal teeth, a blind vein‐ending usually extends toward or terminates directly below the sinus between two adjacent marginal teeth. There appears to be no correlation between the occasional formation of rudimentary marginal teeth and the development of blind vein‐endings. It is concluded that a well‐developed unbranched blind ending morphologically represents one of the vascular strands derived from a normal vein‐dichotomy. The smaller blind endings, associated with terminal vein‐dichotomies, are more difficult to interpret and possibly may represent “supernumerary” veinlets. The parallelism in topography between the blind endings in the leaves of Kingdonia and Circaeaster is briefly discussed, and attention is also drawn to the occurrence of similar blind endings in the dichotomous venation patterns of perianth‐segments and petals of certain angiosperms.