Dichotomous Venation Research Articles

Types of Blind Vein-Endings in the Dichotomous Venation of Circaeaster

Types of Blind Vein-Endings in the Dichotomous Venation of Circaeaster

The complex of Fixcus Deltoidea ; A recent invasion of the sunda shelf

A detailed account of the complex of F. deltoidea Jack and F. oleaefolia King is given in order that its problems may be taken up in the field. Thirteen varieties of F. deltoidea are distinguished, eight of F. oleaefolia . The link between them is F. deltoidea v. motleyana (Miq.) Corner. Clear evolutionary trends to very small figs and leaves and to dichotomous venation supply the evidence for the conclusions that the most reduced state F. deltoidea v. angustifolia (Miq.) Corner is the most widely spread; that the complex advanced into the lowland and mountain forests of the Sunda Shelf from Borneo; that the original connexion was with the ancestors of ser. Podosyceae Corner in the Philippines; that the large seed is a primitive retention; that the complex did not evolve through vicarious disruption of a widespread ancestor; and that, as a recent development of Ficus , possibly still in the making, it represents most clearly the manner of speciation and geographical distribution prevalent in the genus. New taxa: F. deltoidea Jack var. kinabaluensis (Stapf) Corner, F. oleaefolia King var. linearifolia Corner and var, valida Corner.

COMPARATIVE ANATOMY OF THE SEED COATS OF GNETUM AND THEIR PROBABLE EVOLUTION

The seed coats of Gnetum gnemon L., G. ula Brongn., G. montanum f. parvifolium (Warb.) Mgf. and G. neglectum Bl. consist of three layers. The outer layer or sarcotesta is mostly parenchyma but contains some sclereids and fibers and a series of simple vascular bundles. The middle sclerotesta forms masses of sclereids in varying shapes and numbers, sometimes extending as a basal plate, and is usually thicker near the micropylar tube. The second layer also contains a series of small vascular bundles that reach the apex. Depending on the species, the middle layer is sometimes nearly free from the outer layer, may be partially fused with it, or completely fused to it at maturity. The innermost layer of the seed coat constitutes the endotesta which is membranous and only rarely contains sclerenchyma. It possesses a dichotomous venation system with varying degrees of anastomosing, depending upon the species. The above species show qualitative and quantitative differences in their sclerenchyma and laticifers. Seed coat anatomy may be useful in the diagnosis of some species. The trends of evolution of seed coat structure within these four species of Gnetum are discussed, and a comparison of tissue layers and vasculature with certain fossil pteridosperms is made, especially in the Trigonocarpales

Comparative Anatomy of the Seed Coats of Gnetum and Their Probable Evolution

The seed coats of Gnetum gnemon L., G. ula Brongn., G. montanum f. parvifolium (Warb.) Mgf. and G. neglectum Bl. consist of three layers. The outer layer or sarcotesta is mostly parenchyma but contains some sclereids and fibers and a series of simple vascular bundles. The middle sclerotesta forms masses of sclereids in varying shapes and numbers, sometimes extending as a basal plate, and is usually thicker near the micropylar tube. The second layer also contains a series of small vascular bundles that reach the apex. Depending on the species, the middle layer is sometimes nearly free from the outer layer, may be partially fused with it, or completely fused to it at maturity. The innermost layer of the seed coat constitutes the endotesta which is membranous and only rarely contains sclerenchyma. It possesses a dichotomous venation system with varying degrees of anastomosing, depending upon the species. The above species show qualitative and quantitative differences in their sclerenchyma and laticifers. Seed coat anatomy may be useful in the diagnosis of some species. The trends of evolution of seed coat structure within these four species of Gnetum are discussed, and a comparison of tissue layers and vasculature with certain fossil pteridosperms is made, especially in the Trigonocarpales

Further Morphological Studies on Anastomoses in the Dichotomous Venation of Circaeaster

Further Morphological Studies on Anastomoses in the Dichotomous Venation of Circaeaster

MORPHOLOGY OF ANASTOMOSES IN THE DICHOTOMOUS VENATION OF CIRCAEASTER

Anastomoses are very infrequent in the dichotomous venation of Circaeaster agrestis, and no examples of a leaf with more than a single anastomosis were found in a comprehensive study of herbarium and cultivated specimens. The anastomoses are classified into three principal morphological types. In Type I, the adjacent convergent branches of two vein‐dichotomies become confluent for a very short distance and then separate and extend without branching into corresponding teeth of the lamina margin. Except for the short area of union between the two xylem strands, Type I anastomoses resemble vein approximations. The latter represent the close juxtaposition, without xylem‐fusion, of the branches of adjacent vein‐dichotomies. In Type II anastomoses, the inner branches of two neighboring vein‐dichotomies converge and by means of a permanent union, form a single excurrent vein which terminates in a marginal tooth. The distinctive feature of Type III anastomoses is the formation of a very short “commissural vein” which interconnects the closely adjacent branches of two vein‐dichotomies. Cleared leaves revealed that the two veins which fuse in Type II anastomoses may have equally well‐developed xylem strands or one of the branches may be vestigial in structure or entirely devoid of tracheary elements. The xylem of the “commissural vein” in Type III anastomoses consists of one or several tracheary elements which often produce a rather tenuous connection between the two veins. A brief discussion is given of some of the morphogenetic questions posed by the sporadic anastomoses in Circaeaster. The significance of anastomoses with reference to the phylogeny of the dichotomous venation is also considered. Although the anastomoses seem morphologically comparable with the vein‐unions in certain primitive members of the Pteropsida, these resemblances are probably indicative of parallel evolution rather than of the actual nature of the venation in the remote ancestors of Circaeaster.

Morphology of Anastomoses in the Dichotomous Venation of Circaeaster

Morphology of Anastomoses in the Dichotomous Venation of Circaeaster

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.

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.

Ontogeny of the Closed Dichotomous Venation of Regnellidium

Pray, Thomas R. (U. South. California, Los Angeles.) Ontogeny of the closed dichotomous venation of Regnellidium. Amer. Jour. Bot. 49(5): 464–472. Illus. 1962.—The venation of the pinna of Regnellidium consists of a flabellate series of dichotomizing vascular strands, branches of a single pinna trace. At the laminal margin, the entire venation is closed by a marginal vein. The development of the pinna was investigated primarily by means of paradermal sections. During early development, the organization of the marginal meristem and its derivatives is very similar to that previously described for Nephrolepis. The arrangement of cells in the embryonic pinna is predisposed for the differentiation of dichotomizing procambial strands. During the final phases of pinna development, the marginal meristem is altered in such a manner as to result in a submarginal band of elongated cells which differentiates a marginal procambial strand connecting the tips of the dichotomizing veins. Relatively late in pinna ontogeny and after the entire procambial venation pattern has been delimited, the marginal meristem becomes inactive. The possible correlation between extended marginal growth and dichotomizing veins is discussed.

ONTOGENY OF THE CLOSED DICHOTOMOUS VENATION OF REGNELLIDIUM

Pray, Thomas R. (U. South. California, Los Angeles.) Ontogeny of the closed dichotomous venation of Regnellidium. Amer. Jour. Bot. 49(5): 464–472. Illus. 1962.—The venation of the pinna of Regnellidium consists of a flabellate series of dichotomizing vascular strands, branches of a single pinna trace. At the laminal margin, the entire venation is closed by a marginal vein. The development of the pinna was investigated primarily by means of paradermal sections. During early development, the organization of the marginal meristem and its derivatives is very similar to that previously described for Nephrolepis. The arrangement of cells in the embryonic pinna is predisposed for the differentiation of dichotomizing procambial strands. During the final phases of pinna development, the marginal meristem is altered in such a manner as to result in a submarginal band of elongated cells which differentiates a marginal procambial strand connecting the tips of the dichotomizing veins. Relatively late in pinna ontogeny and after the entire procambial venation pattern has been delimited, the marginal meristem becomes inactive. The possible correlation between extended marginal growth and dichotomizing veins is discussed.

MORPHOLOGY AND DICHOTOMOUS VASCULATURE OF THE LEAF OF KINGDONIA UNIFLORA

Foster, Adriance S. (U. California, Berkeley), and Howard J. Arnott. Morphology and dichotomous vasculature of the leaf of Kingdonia uniflora. Amer. Jour. Bot. 47 (8): 684–698. Illus. 1960.—An intensive study of the nodal anatomy, petiolar vasculature and open dichotomous venation of the leaf of Kingdonia has revealed a type of foliar vascular system of unusual morphological and phylogenetic interest. The vascular supply at the nodal level consists of 4 collateral traces which diverge from a single gap into the sheathing leaf base. This type of nodal anatomy is perhaps primitive, and comparisons are made with the unilacunar nodes and the 2‐ and 4‐parted leaf trace systems characteristic of many angiospermous cotyledons and the foliage leaves of certain woody ranalian genera. The petiole of Kingdonia is vascularized by 2 pairs of bundles which represent the upward continuation of the 4 leaf traces. A transition from an even (4) to an odd (3) number of strands occurs near the point of attachment of the 5, lobed, cuneiform lamina segments to the petiole. Each of the 2 abaxial bundles dichotomizes and the central derivative branches fuse to form a double bundle which enters the base of the median lamina segment. The 2 adaxial petiolar bundles diverge right and left into the bases of the paired lateral segments of the lamina. An analogous type of transition from an even to an odd number of veins occurs in many angiospermous cotyledons which develop a definable mid‐vein. But, in Kingdonia, the bundles which enter the bases of the lamina segments give rise to systems of dichotomizing veinlets devoid of “mid‐veins.” Although the majority of the terminal veinlets enter the marginal teeth of the lamina segments, “blind” endings, unrelated to the dentations, occur in all the leaves studied. Typically, all of the vein endings in a given lobule of a lamina segment are derived from the same dichotomous vein system. However, in some leaves, a veinlet dichotomizes directly below a sinus and the branches diverge into the marginal regions of 2 separate lobules. The phylogenetic significance of the occurrence of open dichotomous venation in such an herbaceous angiosperm as Kingdonia is briefly discussed. From a purely morphological viewpoint, the Kingdonia type of venation invites direct comparison with the venation of Sphenophyllum, certain ferns or Ginkgo rather than with any of the known reticulate venation patterns of modern angiosperms. Although the foliar venation of Kingdonia may represent the result of evolutionary reversion, the very rare anastomoses which occur seem primitive in type rather than “vestiges” of a former system of closed venation.

Ontogeny of the Open Dichotomous Venation in the Pinna of the Fern Nephrolepis

Pray, Thomas r. (U. South. California, Los Angeles.) Ontogeny of the open dichotomous venation in the pinna of the fern Nephrolepis. Amer. Jour. Bot. 47(5) : 319—328. Illus. 1960.–The venation of the pinna of Nephrolepis consists of a midvein and 2 lateral series of dichotomizing veins all of which terminate freely near the margins. The development of the pinna is analyzed with particular attention to the nature of the marginal meristem and the organization of the embryonic pinna as it appears in paradermal section. The arrangement of cells in pinna wings during the period of marginal growth displays a pattern which foreshadows the pattern of the mature venation. In contrast with the development of the leaves of angiosperms, marginal growth continues into a relatively late phase of pinna ontogeny and apparently is active throughout the phases of ontogeny concerned with blocking-out the pathways of procambial differentiation. Thus the pattern of venation appears to be correlated with the manner of activity of the marginal meristem and subsequent orientation of its derivatives. The theoretical aspects of the result of this investigation are discussed in relation to other studies of foliar venation ontogeny.

ONTOGENY OF THE OPEN DICHOTOMOUS VENATION IN THE PINNA OF THE FERN NEPHROLEPIS

Pray, Thomas r. (U. South. California, Los Angeles.) Ontogeny of the open dichotomous venation in the pinna of the fern Nephrolepis. Amer. Jour. Bot. 47(5) : 319—328. Illus. 1960.–The venation of the pinna of Nephrolepis consists of a midvein and 2 lateral series of dichotomizing veins all of which terminate freely near the margins. The development of the pinna is analyzed with particular attention to the nature of the marginal meristem and the organization of the embryonic pinna as it appears in paradermal section. The arrangement of cells in pinna wings during the period of marginal growth displays a pattern which foreshadows the pattern of the mature venation. In contrast with the development of the leaves of angiosperms, marginal growth continues into a relatively late phase of pinna ontogeny and apparently is active throughout the phases of ontogeny concerned with blocking‐out the pathways of procambial differentiation. Thus the pattern of venation appears to be correlated with the manner of activity of the marginal meristem and subsequent orientation of its derivatives. The theoretical aspects of the result of this investigation are discussed in relation to other studies of foliar venation ontogeny.

VI.—The Anatomy and Affinity of Stromatopteris moniliformis, Mett

In the year 1861 the ferns collected by Vieillard in the island of New Caledonia were described by Mettenius in a paper entitled “Filices Novæ Caledoniæ” (Ann. Sc. Nat., iv, 15). Among the organisms described was a new and remarkable fern for the reception of which a new Gleicheniaceous genus Stromatopteris was founded. Having noted in particular the absence of roots, and the hairy and sclerotic character of the axis, Mettenius figured the latter as obliquely ascending at its base, but as upright and closely and repeatedly branched more distally. The simply pinnate unbranched leaf was described as a direct continuation of a branch of the axis, with nodular base, slender rachis, and many small leathery pinnæ with sympodial dichotomous venation. With regard to the sori, attention was directed in particular to their development singly on the pinnæ and towards the base of the upper margins, and to the mound-like hairy receptacle which lodged the forking of the basal acroscopic vein. The sporangia, numbering from two to six, were stated to be distributed on the back and towards the periphery of the receptacle; their stalks were short and massive, the annulus complete and transverse, and dehiscence longitudinal and extrorse.

VIII. On “Transfusion-tissue”: its Origin and Function in the Leaves of Gymnospermous Plants.

Summary. The chief points to be gathered from the investigation into the subject of this paper are the following:— 1The universal presence of transfusion-tissue in the leaves of Gymnosperms whose venation is of a reduced or rudimentary character, and where the complex reticulate or dichotomous venation of the Ferns or the higher Angiosperms is lacking. 2The conspicuous development of centripetal xylem in the vascular bundles of the foliage-leaves of all modern Cycads, without exception, where it constitutes the most important part of the xylem of the bundle. This is a point which has long been familiar to botanists. 3The discovery, for the first time, of a mesarch structure of the vascular bundle in the leaves of Coniferae. In the cotyledonary bundles of Ginkgo biloaa, Linn., where this was first observed, the centripetal xylem forms the chief part of the woody strands and is very conspicuously developed. In the bundles of the cotyledons and mature leaves of all other Coniferae which were examined the centripetal xylem is extremely reduced, this reduction having, in most cases, corresponded with a greater development of the centrifugal xylem. It is most obviously present in those genera which approach nearest to Ginkgo in general relationship, such as Cephalotaxus and Taxus. In many genera, however, no trace of this tissue could by discovered, at least in the sections examined, though it is not improbable that isolated remnants of it may occur here and there along the course of the bundle through the leaf. 4The occurrence, in the cotyledonary bundles of Ginkgo biloba, Linn., and Cycas revoluta, Thunb., of an intimate union and gradual transition between the tracheides of the centripetal xylem on the one hand and those of the transfusion-tissue on the other; whence it may be justly inferred that the latter tissue owes its origin, wherever it may subsequently be found, directly to the former. Though in the leaves of the majority of Coniferae this origin is by this time almost entirely obscured, owing to the more or less complete obliteration of the centripetal xylem, it is still often evidenced by the presence of transfusion-tissue on the ventral side of the xylem, by the very frequent extension of the lateral transfusion-tissue towards the ventral side of the bundle, and by the transitions in the characters of the tracheides between those most externally placed and those nearest the protoxylem. In the foliage-leaves of Cycas the connection bet?veen the two tissues is obvious. 5The final inference, that transfusion-tissue, which occurs almost universally in the leaves of Gymnospermous plants as an auxiliary conducting-system, has been phylogenetically derived from the centripetally-formed xylem of the vascular bundle, and is thus, morphologically, an integral portion of the bundle itself. I am indebted to Mr. C. P. Robertson-Glasgow for the use of some excellent preparations of the cotyledons, leaves, &c., of various Coniferous plants. My best thanks are also due to Dr. D. H. Scott for many invaluable criticisms and much kind assistance during the progress of my work. [The important discovery, quite recently made by the two Japanese botanists, Hirase and Ikeno, of spermatozoids in the pollen-tubes of Cycas revoluta, Thunb., and Ginkgo biloba, Linn., and still more recently by Webber in a species of Zamia, bridges over in a striking manner the gulf, hitherto supposed to exist between flowerless and flowering plants, between Ferns or Fern-like plants and Gymnosperms. The relation between the two great groups of plants had already been partly indicated by the Fern-like foliage of such a Cycad as Stangeria. One of the most important of the facts brought forward in the present paper, viz. the occurrence of centripetal xylem in the cotyledonary bundles of both Ginkgo biloba, Linn., and Cycas revoluta, Thunb., seems to me (especially in view both of the external characters and anatomical structure of such fossil forms as the Medulloseae, Lyginodendron, and Nggerathia) to strongly support the above conclusion that Ginkgo and the Cycads hold an intermediate position between some primitive group or groups of Fern-like plants and modern Gymnosperms.