THE ORGANIZATION OF THE VASCULAR SYSTEM IN THE STEMS OF THE NYMPHAEACEAE. III. VICTORIA AND EURYALE

Organization of the stem vascular system was analyzed in Victoria species and Euryale ferox. The stem vascular system consists of a number of concentrically-organized continuing axial stem bundles. At the node each leaf is supplied with a root trace, two lateral leaf traces, and a median leaf trace. A peduncle fusion bundle is also present at each node. The peduncle fusion bundle supplies vascular tissue to the median leaf trace and to the peduncle trace. Flowers are nonmedian axillary but have specific vascular, spatial, and developmental relationships to leaves in a manner that resembles the genus Nymphaea. On the basis of the analysis of the stem vascular system, Victoria and Euryale are more similar to each other than to Nymphaea. However, the vascular system in Victoria and Euryale is similar enough to Nymphaea to suggest that Nymphaea, Victoria, and Euryale form a natural taxon of unique angiosperms. The organization of the stem vascular system in Victoria and Euryale is dicotyledonous.     

THE ORGANIZATION OF THE VASCULAR SYSTEM IN THE STEMS OF THE NYMPHAEACEAE. I. NYMPHAEA SUBGENERA CASTALIA AND HYDROCALLIS

The vascular system in the stems of Nymphaea odorata and N. mexicana subgenus Castalia, and N. blanda subgenus Hydrocallis consists of continuing axial stem bundles with eight being the usual number. The stem bundles are concentric and xylem maturation is mesarch. Xylem elements consist of tracheids with spirally or weakly reticulated secondary wall thickenings. The phloem is made up of companion cells and short sieve tube members with simple sieve plates that are nearly transverse. At the node each leaf is supplied with two lateral leaf traces and a median leaf trace. A root trace is also present and supplies a series of adventitious roots borne on the leaf base. Flowers and vegetative buds develop directly from the apical meristem and occupy leaf sites in a single genetic spiral. Each flower or vegetative bud is related to a leaf through specific spatial and vascular association. The related leaf is separated from the related flower by three members of the genetic spiral and occupies an adjacent orthostichy. Vascular tissue for the related flower arises from the inner surfaces of the four stem bundles supplying leaf traces to the related leaf and extends through the pith to the flower or vegetative bud via a peduncle fusion bundle. The vascular system organization in the investigated species of Castalia and Hydrocallis is not typically monocotyledonous or dicotyledonous, nor can it be considered transitional between them. The ontogeny of the vascular system is similar to typical dicotyledons and the investigated species of Nymphaea can, therefore, be considered to represent highly specialized and modified dicotyledons.     

VASCULAR ORGANIZATION IN SHOOTS OF CACTACEAE. I. DEVELOPMENT AND MORPHOLOGY OF PRIMARY VASCULATURE IN PERESKIOIDEAE AND OPUNTIOIDEAE

Primary shoot vasculature has been studied for 31 species of Pereskioideae and Opuntioideae from serial transections and stained, decorticated shoot tips. The eustele of all species is interpreted as consisting of sympodia, one for each orthostichy. A sympodium is composed of a vertically continuous axial bundle from which arise leaf- and areole-trace bundles and, in many species, accessory bundles and bridges between axial bundles. Provascular strands for leaf traces and axial bundles are initiated acropetally and continuously within the residual meristem, but differentiation of procambium for areole traces and bridges is delayed until primordia form on axillary buds. The differentiation patterns of primary phloem and xylem are those typically found in other dicotyledons. In all species vascular supply for a leaf is principally derived from only one procambial bundle that arises from axial bundles, whereas traces from two axial bundles supply the axillary bud. Two structural patterns of primary vasculature are found in the species examined. In four species of Pereskia that possess the least specialized wood in the stem, primary vascular systems are open, and leaf traces are mostly multipartite, arising from one axial bundle. In other Pereskioideae and Opuntioideae the vascular systems are closed through a bridge at each node that arises near the base of each leaf, and leaf traces are generally bipartite or single. Vascular systems in Pereskiopsis are relatively simple as compared to the complex vasculature of Opuntia, in which a vascular network is formed at each node by fusion of two sympodia and a leaf trace with areole traces and numerous accessory bundles. Variations in nodal structure correlate well with differences in external shoot morphology. Previous reports that cacti have typical 2-trace, unilacunar nodal structure are probably incorrect. Pereskioideae and Opuntioideae have no additional medullary or cortical systems.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE SENSU LATO. XVII. FLORAL ANATOMY OF ONDINEA PURPUREA SUBSPECIES PURPUREA (NYMPHAEACEAE)

Classification and phylogeny of the Nymphaeaceae are unresolved. This study provides floral anatomical data that will assist in elucidating generic interrelationships and systematic relationships to other taxa of angiosperms. The floral anatomy of Ondinea purpurea den Hartog subsp. purpurea has been examined utilizing light microscopy. The peduncle possesses stelar vascular bundle complexes and cortical vascular bundles. Cortical bundles terminate within the peduncle. Each bundle complex consists of 2 collateral bundles on the same radius, the inner bundle inverted; 2 protoxylary lacunae occur yet differ in structure and function. Progressing acropetally, the inner xylary lacunae become discrete mesarch strands surrounded centrifugally by a vascular cylinder formed by divisions and anastomosing of the bundle complexes. Together these become the massive receptacular vascular plexus. The plexus provides collateral traces to the floral organs. Each sepal receives 3 traces that separate from the plexus as 1–3 lateral traces. Petals are absent and no vestigial petal traces have been observed. Distally, the plexus forms several large strands of connate gynoecial and androecial traces termed the principal vascular bundles (PVBs). Ventral veins separate from the PVBs and the latter extend acropetally through the outer ovary wall. Branches of the ventrals and PVBs contribute to septal vascular reticula from which each ovule is supplied by one vascular bundle. Each stamen receives 1 trace from branches of the PVBs. The ventrals and PVBs terminate within the carpellary lobes. A comparative anatomical study is offered that supports the inclusion of Ondinea in the Nymphaeaceae sensu stricto.     

SHOOT VASCULAR SYSTEM AND PHYLLOTAXIS OF CASUARINA (CASUARINACEAE)

In species of Casuarina with multileaved whorls, each stem vascular bundle divides radially into two at the site of a leaf trace separation, and the same two bundles rejoin acropetally to where the trace supplies a leaf. Such divisions are divisions of a single vascular bundle, and the rejoining of bundles forms a single bundle. Proposals that the extant primary vascular systems of dicotyledons may have been derived as in conifers are incorrect in so far as Casuarina is concerned, or the system has evolved beyond that so far proposed for dicotyledons. Reasons are offered, however, for considering that fernlike leaf gaps are not present. Leaf traces supply leaves at the first nodes distal to their origins. The ways by which an increase or decrease of stem bundles occur are described. Phyllotactic patterns range from helical (rare) to whorled. In the embryo, where leaves occur decussately, of certain species with multileaved whorls, and in the shoot apices of species with tetramerous whorls, slight differences in the levels of leaf attachments and the bending of leaf traces indicate the probable evolution of extant whorled phyllotaxies from one or more helical arrangements. Stages in the evolution are suggested. The leaves in most species with multileaved whorls are in true whorls. The original periderm of branchlets lies internally to the internodal traces and chlorenchyma, but is otherwise external to the vascular system. It is concluded that each leaf originates at its level of separation from the axis despite several structural features suggesting that the leaf bases have become congenitally adnate to the stem.     

COMPARATIVE MORPHOLOGY OF THE PRIMARY VASCULAR SYSTEMS IN SOME SPECIES OF ROSACEAE AND LEGUMINOSAE

The structural patterns of the primary vascular systems in some species of Leguminosae and Rosaceae have been determined by tracing the longitudinal course of the vascular bundles in terminal stem segments. These systems are interpreted as consisting of sympodia. Each sympodium is composed of an axial bundle which is continuous through the length of the segment and from which arise trace bundles that supply leaves and axillary buds. A compact arrangement of vascular bundles seems to correlate with the woody habit. Regardless of the degree of compactness of the primary vascular system, the structural identity of the individual sympodia is maintained. The total number of vascular bundles at a particular level is related to the number of axial bundles in the system, the number of traces per leaf and per axillary bud, and the number of internodes traversed by the traces prior to entering a lateral appendage. Shrubs and trees have more vascular bundles than herbs. Data from this study and the literature indicate that the vascular system is predominantly of the open type in dicotyledonous plants which have helically arranged leaves and, further, that in such plants with a 3-trace, trilacunar nodal structure, the number of sympodia coincides with the number of orthostichies (which is also the denominator of the phyllotactic fraction). In open systems leaf gaps cannot be morphologically delimited. Because of the resemblance of the open type of angiosperm vascular system to that of certain gymnosperms, previously interpreted to have evolved from a protostele, we suggest that the eustele of angiosperms is homologous with the stele of gymnosperms. We believe, also, that angiosperms, like gymnosperms, are probably not characterized by leaf gaps of filicinean type. We provide, furthermore, a rationale for the view that the axial bundle of a sympodium is a cauline structure.     

VASCULAR PATTERNS IN STEMS OF THE CYCLANTHACEAE

A survey was made of the distribution of stem vascular bundles in representatives of ten genera of the tropical monocotyledonous family Cyclanthaceae. Films of series of serial transverse sections were used to reconstruct the stem vasculature. Each leaf trace, followed in a basipetal direction from its level of insertion at the stem periphery, describes an obliquely downward course, initially contacting from 1 to 4 (or more) existing axial bundles. The associated bundles form a compound vascular bundle in which the original bundles initially remain discrete, most commonly in a tetrapolar arrangement, with four separate strands. Followed further in the basipetal direction, the strands eventually fuse partly or completely, usually to form a collateral or amphivasal axial bundle which participates in a new structural cycle. Quantitative variation between different taxa includes a simple pattern in Ludovia, in which only bipolar bundles are developed. More elaborate forms have multipolar bundles with more than four separate strands. A systematically useful observation is that stem vasculature in Cyclanthus, representing the subfamily Cyclanthoideae, does not differ significantly from that in subfamily Carludovicoideae although there are some distinctive structural features.     

VASCULAR CONSTRUCTION AND DEVELOPMENT IN THE AERIAL STEM OF PRIONIUM (JUNCACEAE)

The aerial stem of Prionium has been studied by motion-picture analysis which permits the reliable tracing of one among hundreds of vascular strands throughout long series of transverse sections. By plotting the path of many bundles in the mature stem, a quantitative, 3-dimensional analysis of their distribution has been made, and by repeating this in the apical region an understanding of vascular development has been achieved. In the mature stem axial continuity is maintained by a vertical bundle which branches from each leaf trace just before this enters the leaf base. Lateral continuity results from bridges which link leaf traces with nearby vertical bundles. Development of the provascular system involves a meristematic cap into which the blind ends of vertical bundles can be followed. Leaf traces are produced continuously in association with developing leaf primordia for a period of over 30 plastochrones; they connect with the vertical bundles in the meristematic cap and so establish the essential vascular configuration which is later reorientated through about 90° by overall growth of the crown. The last bundles to differentiate from the leaf do so outside the meristematic cap and thus fail to make contact with the axial system; they appear in the mature axis as blind-ending cortical bundles. Prionium is only distantly related to palms and its vascular histology is quite different. Nevertheless, the course of vascular bundles and the origin of this pattern in the stem resembles that of a palm. It is suggested that we are examining the fundamental pattern of vascular development in large monocotyledons.     

VASCULARIZATION OF A MULTILACUNAR SPECIES: POLYSCIAS QUILFOYLEI (ARALIACEAE) I. THE STEM

The odd-pinnate leaves of Polyscias quilfoylei have a sheathing leaf base that completely encircles the stem. At each node, many traces depart the vascular cylinder and traverse an obliquely upward course through the leaf base before aggregating in the rachis. Lateral traces diverge from parent traces in the stem vasculature at variable times relative to the leaf they serve, from variable positions in the vascular cylinder and from parent traces of variable ages. The stem vasculature is formed by the coalescing of leaf traces from as many as five leaves. All bundles departing the vascular cylinder at a node to serve a leaf are true leaf traces originating independently in the stem. Leaf traces develop acropetally from their positions of origin on parent traces. Primordial leaves are first served by the median trace and later by lateral traces. Many traces were recognized in the internodes subtending embryonic leaves, but they could not be related either to a specific leaf or to a specific position within a leaf. Because these traces had not yet achieved contact with a primordial leaf site, they were assumed to be in the process of developing acropetally at the time of sampling. Observations suggest that the multiple traces in this species might perform a similar function of integrating the vascular cylinder that subsidiary bundles perform in certain uni- and trilacunar species.     

VASCULARIZATION OF DEVELOPING LEAVES OF GLEDITSIA TRIACANTHOS L. I. THE NODE,RACHIS, AND RACHILLAE

Leaves of Gleditsia triacanthos L. are served by three leaf traces that subdivide in the node to produce subsidiary bundles. The subsidiary bundles differentiate basipetally in the stem and acropetally in the petiole using the original leaf trace bundles (those that developed acropetally) as templates for their development. Within the pulvinus, the acropetal bundle components merge to form the rachis vasculature consisting of a semicircular arc and a ventral chord; several small bundles diverge to form ventral ridge bundles. Mixing of bundles occurs during vascularization of the lateral rachillae axes. Each diverging rachilla axis receives bundles from the semicircular arc, the ventral chord, and a ridge bundle in a relatively reproducible and predictable pattern. During this process the main rachis vasculature is gradually depleted, but the ridge bundles are reconstituted following divergence of each rachilla pair. The distal rachilla pair is vascularized by a bilateral partitioning of the entire rachis vasculature; a remnant of the central leaf trace terminates in a subulate terminal appendage. Vascularization of the bipinnate G. triacanthos leaf is compared to that of the simple Populus deltoides leaf.     

COMPARATIVE ANATOMY OF THE PETIOLE AND INFRAGENERIC RELATIONSHIPS IN JATROPHA (EUPHORBIACEAE)

Anatomical features of the petiole in several species of Jatropha L. (Euphorbiaceae) are presented as evidence in support of infrageneric relationships. A trilacunar 3-trace nodal pattern is typical for the genus. The vascular supply to the stipules is derived from the branching of the two peripheral leaf traces. The number of vascular bundles range from 11 through 9, 7, 5 and 3, and occur in a ring, as free traces, a medullated cylinder, or as U-shaped free traces. The reduction from nine to three bundles is correlated with the gross morphological features while 11, which occurs only in the section Peltatae (Pax) Dehgan & Webster, presents an increase. Reduction in the number of petiolar traces follows the evolutionary advancement of various taxa. This reduction in traces corresponds with south-north distribution of the species and consequential adaptation to colder and more arid climates in Central America and Africa. Smaller leaves, fewer primary veins and fewer vascular traces have resulted as a response to reduced need for water. Presence of dorsal (super-numerary) bundles which supply the petiolar glands in subgenus Jatropha (= Adenoropium Pax) is considered significant, since African taxa of the section (subsection Pubescentes Pax) have retained these bundles despite the loss of petiolar glands. The latter glands are prominent in the South American and Indian species. Sectional lines in the genus can, therefore, be drawn generally on the basis of numerical constancy and relative uniformity in the arrangement of petiolar traces. The continuity of vascular bundles from the stem into the petiole and variations of bundle arrangements are depicted in three-dimensional drawings.     

VASCULAR ANATOMY OF THE NODAL REGION IN POPULUS DELTOIDES BARTR

The ontogeny of vascular bundles in the nodal region of Populus deltoides Bartr. was examined to understand more thoroughly the structure-function relation between leaf and stem. Three vascular traces from the stem independently enter each leaf in the nodal region. At the base of each developing leaf a region was observed in which both bundle size and vascular development was reduced; this region was referred to as the constricted zone. The constricted zone was described quantitatively at 13 locations within the nodal region of a leaf at LPI 5 by determining the number of metaxylem vessels and the total metaxylem vessel area in each of the three leaf traces. A plot of these data showed a distinct minimum value for total metaxylem vessel area within the constricted zone of each trace; the location of this minimum value was referred to as the constriction plane. Each vascular bundle within the nodal region is composed of independent subsidiary bundles that originate within the constricted zone. These bundles provide a direct connection between the leaf lamina and the stem. The node was defined anatomically on the basis of the ontogenetic development of the subsidiary bundles. The node began at the initial exit point of the central trace from the vascular cylinder and extended distally to the constriction plane. This definition allowed us to quantify the limits of each node. The origin of the initiating layer and metacambium was also examined within the nodal region. These precursors of the cambium develop continuously and acropetally from the stem into the leaf. The developmental implications of the constricted zone and the metacambium within the nodal region are discussed with respect to wood formation.     

MORPHOLOGY AND VASCULATURE OF THE LEAF OF POTATO (SOLANUM TUBEROSUM)

The leaf and stem of the potato plant (Solanum tuberosum L. cv. Russet Burbank) were studied by light microscopy to determine their morphology and vasculature; scanning electron microscopy provided supplemental information on the leaf's morphology. The morphology of the basal leaves of the potato shoot is quite variable, ranging from simple to pinnately compound. The upper leaves of the shoot are more uniform, being odd pinnate with three major pairs of lateral leaflets and a number of folioles. The primary vascular system of the stem is comprised of six bundles, three large and three small ones. The three large bundles form a highly interconnected system through a repeated series of branchings and arch-producing mergers. Two of the three large bundles give rise to short, lateral leaf traces at each node. Each of the small bundles in the stem is actually a median leaf trace which extends three internodes before diverging into a leaf. The three leaf traces enter the petiole through a single gap; thus the nodel anatomy is three-trace unilacunar. Upon entering the petiole, each of the laterals splits into an upper and a lower lateral. Whereas the upper laterals diverge entirely into the first pair of leaflets, the lower laterals feed all of the lateral leaflets through a series of bifurcations. Prior to their entering the terminal leaflet, the lower laterals converge on the median bundle to form a single vascular crescent which progresses acropetally into the terminal leaflet as the midvein, or primary vein. In the midrib, portions of the midvein diverge outward and continue as secondaries to the margin on either side of the lamina. Near the tip of the terminal leaflet, the midvein consists of a single vascular bundle which is a continuation of the median bundle. Six to seven orders of veins occur in the terminal leaflet.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE (SENSU LATO). XIII. CONTRIBUTIONS TO THE VEGETATIVE AND FLORAL STRUCTURE OF CABOMBA

Six species of Cabomba have been examined although the anatomy of the vegetative axes is based on the study of only C. caroliniana and C. palaeformis. A plant consists of an erect short shoot with decussate leaves which bears axillary flowering shoots and rhizomes. A rhizome bears decussate leaves and may also form axillary flowering shoots or turn upward and become a new short shoot. The phyllotaxies of the flowering shoots are proximately decussate or ternate (C. piauhyensis). The flowering shoots with decussate phyllotaxy change to 1/3 phyllotaxy distally; they bear axillary flowers proximally, and extra-axillary flowers distally. Flowering shoots with ternate phyllotaxy do not change distally but each produces first axillary and then extra-axillary flowers. Decussate vegetative axes and flowering shoots have four vascular bundles; ternate vegetative axes and flowering shoots have six vascular bundles, distantly paired into two or three vascular bundle-pairs, respectively. An elliptical vascular plexus occurs at each node. Each leaf receives one bundle-pair from one trace and each flower three bundle-pairs. A two-level receptacular vascular plexus occurs in flowers; the proximal, larger portion provides traces to perianth and stamens and the distal, smaller portion becomes carpellary traces. Each of the three sepals typically receives five branch traces from a basal principal trace, and each of the three petals receives, typically, three branch traces from a basal principal trace. Sepals and petals generally occur in a single, basally connate whorl. Each stamen receives one trace. Each stamen of three-stamen flowers is opposite a petal; each stamen of six-stamen flowers is aligned with an interval between a petal and adjacent sepal. Each staminal trace, which is just above the principal petal trace, in a three-petal flower, is frequently adnate to the latter trace. Each carpel receives one principal trace from the distal, small extension of the receptacular plexus, and each principal trace becomes three conventional veins of a carpel. Ovules may be borne directly over one of the veins or in any position between veins and are supplied by branches of the nearest vein or nearest two veins. All traces, ovular supply veins and the proximal portions of all veins are amphicribral. The several anatomical and morphological differences in vegetative axes and flowers between Cabomba and Brasenia suggest a greater taxonomic distance between the two genera than commonly supposed. It is suggested that extra-axillary flowers in 1/3 helical and ternate flowering shoots of Cabomba might be advantageous in preventing anthesis of flowers beneath peltate leaves. The aberrant position might be the initial evolutionary step toward what, in other nymphaeaceous genera, has shifted each flower to an adjacent helix. It is proposed that the zigzag stem accompanying the trigonal and sympodial flowering shoots may offer greater stability and floatability in water than the monopodial form. Several suggestions are offered for the variability of ovular positions: 1) the variability is a vestige of former laminar placentation in conduplicate carpels; 2) it is a vestige of a primitive condition antedating the current close association of ovules with ventral carpellary veins; 3) it is an early stage of evolution which might have terminated in laminar placentation and cantharophily, but which was replaced by a trend toward myophily.     

DEVELOPMENT AND PHYLLOTAXIS OF THE VEGETATIVE AXILLARY BUD OF MICHELIA FUSCATA

Tucker, Shirley C. (Northwestern U., Evanston, III.) Development and phyllotaxis of the vegetative axillary bud of Michelia fuscata . Amer. Jour. Bot. 50(7): 661–668. Illus. 1963.—The vegetative axillary buds of Michelia fuscala are dorsiventrally symmetrical with 2 ranks of alternately produced leaves. The direction of the ontogenetic spiral in each of these buds is related both to the symmetry of the supporting branch and to the position of the bud along the branch. On a radially symmetrical branch, all the axillary buds are alike—all clockwise, for example. But in a dorsiventrally organized branch the symmetry alternates from clockwise in 1 axillary bud to counterclockwise in the next bud along the axis. Leaf initiation and ontogeny of the axillary apical meristem conform with those of the terminal vegetative bud. The axillary bud arises as a shell zone in the second leaf axil from the terminal meristem. During this process the axillary apex develops a zonate appearance. The acropetally developing procambial supply of the axillary bud consists wholly of leaf traces. At the nodal level the bud traces diverge from the same gap as the median bundle trace of the subtending leaf. Only the basal 1–2 axillary buds which form immediately after the flowers elongate each year, while the majority remains dormant with 3 leaves or fewer.     

ONTOGENY OF THE STEM-NODE-LEAF VASCULAR CONTINUUM OF AUSTROBAILEYA

Developmental study of the stem-node-leaf vascular continuum of Austrobaileya scandens White reveals that the vasculature within each leaf originates from a single procambial strand, that becomes separated into two strands only at the junction of leaf and stem. At lower levels in the stem the two strands become incorporated into independent portions of the stele. At later stages of development the solitary vascular bundle within the young leaf undergoes considerable lateral growth, resulting in an essentially continuous arc of vascular tissue. Ontogenetic evidence indicates that the vascular bundle in the midrib of the lamina should be regarded as a fundamentally single bundle and not interpreted as two bundles that have undergone various degrees of secondary fusion. A condition of two totally separate bundles extending the entire length of the leaf was not encountered. Our observations confirm the characterization of Austrobaileya as an example of “second rank” level of leaf vasculature. Nodal anatomy emphasizes the extremely isolated taxonomic position of Austrobaileya within the primitive dicotyledons.     

ORGANIZATION AND ONTOGENY OF THE VASCULAR SYSTEM IN THE PETIOLE OF EASTERN COTTONWOOD

The topologic arrangement of petiolar bundles varies within the length of the cottonwood petiole. Each petiolar bundle is formed by the subdivision and aggregation of acropetally differentiating subsidiary bundles in a predictable pattern. The subsidiary bundles provide vascular continuity between the stem and specific portions of the leaf lamina. Spot-labeling of individual veins with ¹⁴CO₂, freeze substitution, and microautoradiography were used to establish the relation between the secondary veins of the lamina and the vasculature of the petiole. Within the petiole vasculature each subsidiary bundle was continuous with a specific portion of the lamina and seemed to have a separate function. Subsidiary bundles continuous with the central leaf trace were closely related functionally to the tip region of the lamina, while the subsidiary bundles continuous with the lateral leaf traces were functionally related to the middle and basal portions of the lamina.     

铁筷子(毛茛科)营养器官的结构及其系统学意义

应用解剖学方法,对铁筷子(Helleborus thibetanusFranch.)(毛茛科)营养器官的结构进行了研究。结果表明,铁筷子根的初生结构观察到三原型、四原型和六原型。营养器官中的维管束在横切面上木质部中的导管分子不呈“V”字形排列;根状茎的次生结构由外向内为表皮、皮层和维管柱,髓射线发达。茎的初生结构中多个维管束排列成环状,维管束鞘分化不明显,节部为单隙三迹,叶迹分别来自于3条维管束或同一条维管束。叶为两面叶,表皮细胞不规则;气孔器只分布于下表皮,为毛茛科典型的无规则型气孔。从铁筷子营养器官的解剖学特点来看,与毛茛科其它植物基本相同,但在营养器官中维管束木质部不呈“V”字形、维管束鞘分化不明显、节部具单叶隙等特征上与其它毛茛科植物不同。     

A COMPARATIVE STUDY OF THE PRIMARY VASCULAR SYSTEM OF CONIFERS. I. GENERA WITH HELICAL PHYLLOTAXIS

The primary vascular system of 23 species belonging to 18 genera of conifers with helical phyllotaxis has been investigated with the intent of determining the architecture of the system. Special attention has been given to nodal and subnodal relations of the vascular bundles. The vascular system seems to be composed solely of relatively discrete sympodia, that is, axial vascular bundles from which leaf traces branch unilaterally. Although the discreteness of the sympodia is not immediately apparent because of their undulation and lateral contacts with neighboring ones, close examination, including a statistical analysis of the tangential contacts, seems to reveal that each sympodium maintains its identity throughout. Although two traces may be apparent at nodal levels, the trace supply to a leaf originates, in all species, as a single bundle. An analysis is made of the relationship between the vasculature and the phyllotaxis. It is observed that the direction of trace divergence can be accurately predicted when the direction of the ontogenetic spiral, the angle of divergence of leaf traces, and the number of sympodia are known.     

The Vascular Pattern of Italian Ryegrass (Lolium multiflorum Lam.): 3. The Leaf Trace System, and Tiller Insertion, in the Adult

The leaf trace system in the region of congested internodesat the base of Lolium multiflorum is described. A typical major trace in a leaf consists of a collateral bundlehaving a double bundle sheath and incorporating a certain amountof sclerenchyma. As such a leaf trace is followed down intothe stem it increases in diameter, loses the inner (mestome)bundle sheath, and the xylem becomes associated with xylem transfercells. Lower down, the bundle diameter is reduced although nowit has become amphivasal. The internal xylem only is still associatedwith transfer cells. The proximal portions of the bundle aremuch reduced, transfer cells, mestome sheath, and sclerenchymaare lacking and the now insignificant bundle merges with a lowerleaf trace or some other vascular tissue. Such a bundle in thestem may be in direct contact via bridges with other leaf traces,with the nodal plexus, and with the peripheral plexus that surroundsthe inner leaf trace system. In the base of a typical young plant, approximately one-halfof all leaf traces, including all the median veins, join bundlesfrom the next oldest leaf. Approximately one-third join thenodal plexus, and the remainder variously join bundles fromthe same or next but one oldest leaf to join the peripheralplexus. The differentiation of tiller insertions into the pre-existingmain stem system is highly variable. In a very young tillera number of traces were seen to terminate before the main systemwas reached suggesting basipetal differentiation. The actualconnections made by the tiller traces may occur with any nearbyleaf trace, the nodal plexus, or with the peripheral plexus.Later differentiating leaf traces in a tiller join leaf tracesof the tiller itself. Occasional bundles from secondary tillers by-pass the vasculartissue of the primary tiller to join directly with that of theparent plant. Vascular connections between parent and tiller,although very variable, appear to be totally comprehensive froma functional standpoint.