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GNETALES

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Originally appearing in Volume V12, Page 764 of the 1911 Encyclopedia Britannica.

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GNETALES .—These are trees or shrubs with See also:

SIMPLE

simple leaves. The See also:

FLOWERS, ARTIFICIAL

flowers are dioecious, rarely monoecious, provided with one or two perianths. The See also:

wood is characterized by the presence of vessels in addition to tracheids. There are no See also:

RESIN (through O.Fr. resine, modern reline, from Lat. resina, prcbably Latinized from Greek Pirivrt, resin)

resin-canals. The three existing genera, usually spoken of as members of the Gnetales, differ from one another more than is consistent with their inclusion in a single See also:

FAMILY

family; we may therefore better See also:

EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express their diverse characters by regarding them as types of three See also:

SEPARATE

separate families—(t) Ephedroideae, genus Ephedra; (2) Welwitschioideae, genus Welwitschia; (3) Gnetoideae, genus Gnetum. Our knowledge of the Gnetales leaves much to be desired, but such facts as we possess would seem to indicate that this See also:

GROUP

group is of See also:

SPECIAL

special importance as foreshadowing, more than any other See also:

GYMNOSPERMS

Gymnosperms, the Angiospermous type. In the more heterogeneous structure of the wood and in the See also:

possession of true vessels the Gnetales agree closely with the higher flowering See also:

PLANTS

plants. It is of See also:

INTEREST

interest to See also:

note that the leaves of Gnetum, while typically Dicotyledonous in See also:

APPEARANCE (from Lat. apparere, to appear)

appearance, possess a Gymnospermous See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character in the continuous and See also:

PLATE

plate-like medullary rays of their vascular bundles. The presence of a perianth is a feature suggestive of an approach to the floral structure of See also:

ANGIOSPERMS

Angiosperms; the prolongation of the integument furnishes the flowers with a substitute for a stigma and See also:

style. The genus Ephedra, with its prothallus and archegonia, which are similar to those of other Gymnosperms, may be safely regarded as the most See also:

PRIMITIVE

primitive of the Gnetales. In Welwitschia also the megaspore is filled with prothallus-See also:

TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue, but single See also:

egg-cells take the See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place of archegonia. In certain See also:

SPECIES

species of Gnetum described by See also:

KARSTEN, KARL JOHANN BERNHARD (1782-1853)

Karsten the megaspore contains a peripheral layer of See also:

PROTOPLASM

protoplasm, in which scattered nuclei represent the See also:

FEMALE

female reproductive cells; in Gnetum Gnemon a similar See also:

state of things exists in the upper See also:

HALF

half of the megaspore, while the See also:

LOWER

lower half agrees with the megaspore of Welwitschia in being full of prothallus-tissue, which serves merely as a See also:

RESERVOIR

reservoir of See also:

food.

Lotsy has described the occurrence of special cells at the See also:

APEX

apex of the prothallus of Gnetum Gnemon,which he regards as imperfect archegonia (fig. 17, C, a) ; he suggests they may represent vestigial structures pointing back to some ancestral See also:

FORM (Lat. forma)

form beyond the limits of the See also:

PRESENT

present group. The Gnetales probably had a separate origin from the other Gymnosperms; they carry us nearer to the Angiosperms, but we have as yet no satisfactory See also:

EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence that they represent a See also:

STAGE (Fr. 6/age; from Lat. stare, to stand)

stage in the See also:

DIRECT

direct See also:

LINE

line of Angiospermic See also:

EVOLUTION

evolution. It is not improbable that the three genera of this See also:

ancient phylum survive as types of a blindly-ending See also:

BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch of the Gymnosperms; but be that as it may, it is in the Gnetales more than in any other Gymnosperms that we find features which help us to obtain a dim prospect of the lines along which the Angiosperms may have been evolved. Ephedra.—This genus is the only member of the Gnetales represented in See also:

EUROPE

Europe. Its species, which are characteristic of warm temperate latitudes, are usually much-branched shrubs. The finer branches are See also:

green, and See also:

bear a See also:

close resemblance to the stems of Equisetum and to the slender twigs of See also:

CASUARINA

Casuarina; the See also:

SURFACE

surface of the See also:

long internodes is marked by See also:

FINE

fine See also:

LONGITUDINAL

longitudinal ribs, and at the nodes are See also:

BORNE, KARL LUDWIG (1786–1837)

borne pairs of inconspicuous See also:

scale-leaves. The flowers are small, and borne on axillary shoots. A single male See also:

flower consists of an See also:

AXIS (Lat. for " axle ")

axis enclosed at the See also:

BASE

base by an inconspicuous perianth formed of two concrescent leaves and terminating in two, or as many as eight, shortly stalked or sessile anthers. The female flower is enveloped in a closely fitting See also:

sac-like investment, which must be regarded as a perianth ; within this is an orthotropous ovule surrounded by a single integument prolonged upwards as a See also:

BEAK (early forms beke and becke, from Fr. bec, late Lat. beccus, supposed to be a Gaulish word; the Celtic bec and beq, however, are taken from the English)

beak-like micropyle. The flower may be described as a bud bearing a'pair of leaves which become fused and constitute a perianth, the apex of the shoot forming an ovule. In See also:

FUNCTION

function the perianth may be compared with a unilocular ovary containing a single ovule; the projecting integument, which at the See also:

time of See also:

POLLINATION

pollination secretes a drop of liquid, serves the same purpose as the style and stigma of an angiosperm.

The megaspore is filled with tissue as in typical Gymnosperms, and from some of the superficial cells 3 to 5 archegonia are See also:

DEVELOPED

developed, characterized by long multicellular necks. The archegonia are separated from one another, as in Pinus, by some of the prothallus-tissue, and the cells next the egg-cells (tapetal layer) contribute food-material to their development. After fertilization, some of the uppermost bracts below each flower become red and fleshy; the perianth develops into a woody See also:

shell, while the integument remains membranous. In some species of Ephedra, e.g. E. altissima, the fertilized eggs grow into tubular proembryos, from the tip of each of which embryos begin to be developed, but one only comes to maturity. In Ephedra helvetica, as described by Jaccard, no proembryo or suspensor is formed; but the most vigorous fertilized egg, after undergoing several divisions, becomes attached to a tissue, termed the See also:

COLUMELLA, LUCIUS JUNIUS MODERATUS

columella, which serves the purpose of a See also:

PRIMARY

primary suspensor; the columella appears to be formed by the lignification of certain cells in the central region of the embryo-sac. At a later stage some of the cells in the upper (micropylar) end of the embryo See also:

DIVIDE

divide and undergo considerable See also:

ELONGATION

elongation, serving the purpose of a secondary suspensor. The secondary wood of Ephedra consists of tracheids, vessels and parenchyma; the vessels are characterized by their wide lumen and by the large simple or slightly-bordered pits on their oblique end-walls. Gnetum.—This genus is represented by several species, most of which are climbing plants, both in tropical See also:

AMERICA

America and in warm regions of the Old See also:

WORLD

World. The leaves, which are borne in pairs at the tumid nodes, are See also:

OVAL (Lat. ovum, egg)

oval in form and have a Dicotyledonous type of venation. The male and female inflorescences have the form of simple or paniculate spikes. The spike of an inflorescence bears whorls of flowers at each See also:

NODE (Lat. nodus, a loop)

node in the axils of concrescent bracts accompanied by numerous sterile hairs (paraphyses); in a male inflorescence numerous flowers occur at each node, while in a female inflorescence the number of flowers at each node is much smaller.

A male flower consists of a single angular perianth, through the open apex of which the flower-axis projects as a slender See also:

COLUMN (Lat. columna)

column terminating in two anthers. The female flowers, which are more complex in structure, are of two types, See also:

COMPLETE

complete and incomplete; the latter occur in association with male flowers in a male inflorescence. A complete female flower consists of a nucellus (fig. 17, A, n), surrounded by a single integument (fig. 17, A, i), prolonged upwards as a narrow See also:

TUBE (Lat. tuba)

tube and succeeded by an inner and an See also:

OUTER

outer perianth (fig. 17, A, p' and p"). The whole flower may be looked upon as an See also:

ADVENTITIOUS (from Lat. adventicius, coming from abroad)

adventitious bud bearing two pairs of leaves; each pair becomes concrescent and forms a perianth, the apex of the shoot being converted into an orthotropous ovule. The incomplete female flowers are characterized by the almost complete suppression of the inner perianth. Several embryo-sacs (megaspores) are present in the nucellus of a See also:

young ovule, but one only attains full See also:

SIZE

size, the smaller and partially developed megaspores (fig. 17, B and C, e) being usually found in close association with the surviving and fully-grown megaspore. In Gnetum Gnemon, as described by Lotsy, a mature embryo-sac contains in the upper See also:

PART

part a large central vacuole and a peripheral layer of protoplasm, including several nuclei, which take the place of the archegonia of Ephedra; the lower part of the embryo-sac, separated from the upper by a constriction, is full of parenchyma. The upper part of the megaspore may be spoken of as the fertile half (fig.

17, B and C, F"). and the lower part, which serves only as food-reservoir for the growing embryo, may be termed the sterile half (fig. 17, B and C, S). (Coulter, See also:

Bet. See also:

GAZETTE

Gazette, xlvi., 1908, regards this tissue as belonging to the nucellus.) At the time of pollination the long tubular 763 integument secretes a drop of fluid at its apex, which holds the See also:

POLLEN, AUGUST (or, as he afterwards called himself, ADOLF) LUDWIG (1794-1855)

pollen-grains, brought by the See also:

wind, or possibly to some extent by See also:

INSECT

insect agency, and by evaporation these are See also:

DRAWN

drawn on to the See also:

TOP (cf. Dan. top, Ger. Topf, also meaning pot)

top of the nucellus, where partial disorganization of the cells has given rise to an irregular pollen-chamber (fig. 17, A, pc). The pollen-tube, containing two generative and one vegetative See also:

NUCLEUS (Lat. for the kernal of a nut, nux, the stone of fruit)

nucleus, pierces the See also:

wall of the megaspore and then becomes swollen (fig. 17, B and C, pt) ; finally the two generative nuclei pass out of the tube and fuse with two of the nuclei in the fertile half of the megaspore. As the result of fertilization, the fertilized nuclei of the megaspore become surrounded by a See also:

CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell-wall, and constitute zygotes, which may attach themselves either to the wall of the megaspore or to the end of a pollen-tube (fig. 17, C, z and z') ; they then grow into long tubes or proembryos, which make their way towards the prothallus (C, z'), and eventually embryos are formed from the ends of the proembryo tubes. One embryo only comes to maturity. The embryo of Gnetum forms an out-growth from the hypocotyl, which serves as a feeder and draws nourishment from the prothallus. The fleshy outer portion of the See also:

SEED (from the root seen in Lat. serere, to sow)

seed is formed from the outer perianth, the woody shell being derived from the inner perianth.

The climbing species of Gnetum are characterized by the See also:

PRODUCTION (Lat. productionem, from producere, to pro-duce)

production of several concentric cylinders of secondary wood and bast, the additional cambium-rings being products of the pericycle, as in Cycas and Macrozamia. The structure of the wood agrees in the See also:

main with that of Ephedra. Welwitschia (Tumboa).—This is by far the most remarkable member of the Gnetales, both as regards See also:

HABIT (through the French from Lat. habitus, from habere, to have, hold, or, in a reflective sense, to be in a certain condition; in many of the English senses the French use habitude, not habit)

habit and the form of its flowers. In a supplement to the systematic See also:

WORK

work of Engler and Prantl the well-known name Welwitschia, instituted by See also:

Hooker in 1864 in See also:

HONOUR (Lat. honos or lwnor, honoris; in English the word was spelled with or without the u indifferently until the 17th century, but during the 18th century it became fashion-able to spell the word " honor "; Johnson's and Webster's Dictionaries stereoty

honour of Welwitsch, the discoverer of the plant, is superseded by that of Tumboa, originally suggested by Welwitsch. The genus is confined to certain localities in See also:

DAMARALAND

Damaraland and adjoining territory on the See also:

west See also:

COAST (from Lat. costa, a rib, side)

coast of tropical See also:

South See also:

Africa. A well-grown plant projects less than a See also:

FOOT

foot above the surface of the ground; the See also:

STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem, which may have a circumference of more than 12 ft., terminates in a depressed See also:

CROWN

crown resembling a circular table with a median groove across the centre and prominent broad ridges concentric with the margin. The thick tuberous stem becomes rapidly narrower, and passes gradually downwards into a tap-See also:

root. A pair of small strap-shaped leaves succeed the two cotyledons of the seedling, and persist as the only leaves during the See also:

LIFE

life of the plant; they retain the See also:

POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power of growth in their basal portion, which is sunk in a narrow groove near the edge of the crown, and the tough lamina, 6 ft. in length, becomes split into narrow strap-shaped or thong-like strips which trail on the ground. Numerous circular pits occur on the concentric ridges of the depressed and wrinkled crown, marking the position of former inflorescences borne in the See also:

LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf-axil at different stages in the growth of the plant. An inflorescence has the form of a dichotomously-branched cyme bearing small erect cones; those containing the female flowers attain the size of a See also:

fir-See also:

CONE (Gr. Kwvos)

cone, and are See also:

SCARLET

scarlet in See also:

COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour. Each cone consists of an axis, on which numerous broad and thin bracts are arranged in See also:

REGULAR

regular rows; in the axil of each bract occurs a single flower; a male flower is enclosed by two opposite pairs of leaves, forming a perianth surrounding a central sterile ovule en-circled by a See also:

RING (O.E. hring; a word common to Teutonic languages; and probably cognate with the Lat. circus, Gr. KtpKOS or KpLKOS, Skt'. chakra, wheel, circle, cf. also " harangue "); in art, a band of circular shape of varying sizes, made of any material and used f

ring of stamens See also:

UNITED

united below, but See also:

FREE

free distally as See also:

SHORT, FRANCIS JOB (1857– )

short filaments, each of which terminates in a trilocular anther. The integument of the sterile ovule is prolonged above the nucellus as a spirally-See also:

TWISTED

twisted tube See also:

EXPANDED

expanded at its apex into a See also:

FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat stigma-like See also:

ORGAN

organ.

A complete and functional female flower consists of a single ovule with two integuments, the inner of which is prolonged into a narrow tubular micropyle, like that in the flower of Gnetum. The megaspore of Welwitschia is filled with a prothallus-tissue before fertilization, and some of the prothallus-cells function as egg-cells; these grow upwards as long tubes into the apical region of the nucellus, where they come into contact with the pollen-tubes. After the egg-cells have been fertilized by the non-motile male cells they grow into tubular proembryos, producing terminal embryos. The stem is traversed by numerous See also:

COLLATERAL (from Med. Lat. collateralis,—cum, with, and latus, lateris, side,—side by side, hence parallel or additional)

collateral bundles, which have a limited growth, and are constantly replaced by new bundles developed from strands of secondary See also:

MERISTEM (Gr. Aquas-6s, divided or divisible)

meristem. One of the best-known anatomical characteristics of the genus is the occurrence of numerous spindle-shaped or branched See also:

fibres with enormously-thickened walls studded with crystals of See also:

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

calcium oxalate. Additional See also:

INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information has been published by See also:

PROFESSOR (the Latin noun formed from the verb profiteri, to declare publicly, to acknowledge, profess)

Professor See also:

Pearson of Cape See also:

TOWN

Town based on material collected in Damaraland in 1904 and 1906–1907. In 1906 he gave an See also:

account of the See also:

early stages of development of the male and female See also:

ORGANS

organs and, among other interesting statements in regard to the See also:

general See also:

BIOLOGY (Gr. Qios, life)

biology of Welwitschia, he expressed the See also:

OPINION (Lat. opinio, from opinari, to think)

opinion that, as I-looker suspected, the ovules are pollinated by insect-agency. In a later See also:

paper Pearson considerably extended our .knowledge of the See also:

REPRODUCTION

reproduction and gametophyte of this genus. AuTnourrIEs.—General: See also:

Bentham and Hooker, Genera See also:

Plan-'arum (See also:

LONDON

London, 1862–1883) ; Engler and Prantl, See also:

Die nati rlichen Pflanzenfamilien (See also:

LEIPZIG

Leipzig, 1889 and 1897) ; Strasburger, Die Consferen and Gnetaceen (See also:

JENA

Jena, 1872) ; Die Angiospermen lend die Gymnospermen (Jena, 1879) ; Histologische Beitrage, iv. (Jena, 1892) ; Coulter and See also:

Chamberlain, See also:

MORPHOLOGY, (Gr. yopdsil, form)

Morphology of Spermatophytes (New See also:

York, 1901); Rendle, The See also:

CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

Classification of Flowering Plants, vol. i. (See also:

CAM (CAO), DIOGO (fl. 1480-1486)

Cam-See also:

BRIDGE

bridge, 1904) ; " The Origin of Gymnosperms " (A discussion at the Linnean Society; New Phytologist, vol. v., 1906). Cycadales: Mettenius, " Beitriige zur Apatomie der Cycadeen," Abh. k. sdchs.

A Fic. 17.—Gnetum Gnemon. (After Lotsy.) A, Female Flower. a, Imperfect Archegonia. e, Partially developed Megaspore. F, Fertile half. S, Sterile half. pt, Pollen-tube. z, Zygote. Prothallus. n, Nucellus. pc, Pollen-chamber. I, Integument. p', Inner Perianth. p", Outer Perianth. B, C, Megaspore.

Ges. Wiss. (186o); Treub, " Recherches sur See also:

les Cycadees," See also:

Ann. Bot. Jard. See also:

BUITENZORG

Buitenzorg, ii. (1884) ; Solms-Laubach, " Die Sprossfolge der Stangeria, &c.," Bot. Zeit. xlviii. (1896) ; Worsdell, " See also:

Anatomy of Macrozamia," Ann. Bot. x. (1896) (also papers by the same author, Ann. Bot., 1898, Trans.

Linn. See also:

Soc. v., 1900) ; See also:

Scott, " The Anatomical Characters presented by the Peduncle of Cycadaceae," Ann. Bot. xi. (1897) ; See also:

Lang, " Studies in the Development and Morphology of Cycadean Sporangia, No. I.," Ann. Bot. xi. (1897); No. II., Ann. See also:

Bat. xiv. (1900); Webber, " Development of the Antherozoids of Zamia," Bot. Gaz. (1897) ; Ikeno, " Untersuchungen fiber die Entwickelung, &c., bei Cycas revoluta," Journ.

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