EVOLUTION OF COTYLEDONARY AND NODAL VASCULATURE IN THE JUGLANDACEAE

Cotyledonary nodal patterns of the Juglandaceae range from 1-gap, 2-trace to multi-gap, multi-trace. The development of increased nodal complexity is associated with at least two independent evolutionary shifts from epigeal to hypogeal germination. The taxa with epigeal germination such as Engelhardia sect. Engelhardia, Engelhardia sect. Psilocarpeae, Platycarya, and Pterocarya all have 1-gap, 2-trace nodes. The change to hypogeal germination in Engelhardia sect. Oreomunnea and Alfaroa is correlated with the development of 1-gap, 3-trace cotyledonary nodes. The second line has led to large, heavy-fruited members with hypogeal germination and complex cotyledonary nodes ranging from 2–6 gaps. The diversity of nodal patterns is the result of variation on a common theme; five basic vascular strands in the cotyledon, undergoing variations in dichotomy, fusion, and separation, are associated with one to many gaps. Presumably the complex development of the cotyledonary node is a response to increased functional demands of hypogeous cotyledons.     

Restionaceae seedlings: Morphology,anatomy and systematic implications

Restionaceae differ from most monocot families in having both epigeal and hypogeal germination. The green cotyledons associated with epigeal germination have a central vascular strand as found in most epigeal monocotyledons. In some genera the cotyledon may have a hairpin‐like structure, also described for Anthericaceae. The cotyledon of the hypogeal seedlings is short, without green pigment and largely remains embedded in the seed coat. Hypogeal germination is correlated with large, woody, indehiscent, frequently myrmecochorous nuts, while epigeal germination is found in species with smaller indehiscent nutlets or seeds, dispersed in a variety of ways. The primitive condition is most likely epigeal germination. In hypogeal seedlings of some African and Australian taxa an epicotyledonary rhizome is found between the primary root and the first leaves. Seedlings of African Restionaceae frequently have elongated culm internodes, whereas in the Australian species studied, internodes are very short, resulting in a cluster of seedling leaves. The leaf blades, which in most species are only found on the seedlings, are very simple anatomically. However, they appear to be unifacial, similar to the leaf blades of Anarthria (Anarthriaceae). The anatomical specialisations in the blades mirror those recorded for the culm anatomy. These observations are consistent with the hypothesis that Centrolepidaceae may be neotonous Restionaceae. They also corroborate the morphology of the African Restionaceae, and the presently accepted phylogeny of the African genera of Restionaceae.     

ONTOGENY OF MAJOR VEINS IN THE LAMINA OF POPULUS DELTOIDES BARTR

The ontogeny of the major venation in the lamina of Populus deltoides Bartr. leaves was investigated in relation to the development of original procambial bundles, subsidiary bundles, and their derivatives. Serial sections and clearings were used to show that the midrib region is a composite structure consisting of several independent vascular bundles, each of which eventually diverges into the lamina to become a secondary vein. The sequence of events in the ontogeny of major secondary veins is: (1) an original procambial strand develops acropetally and becomes the precursor of the first vascular bundle of the midrib region of the lamina, (2) ground tissue at the forefront of acropetally developing subsidiary procambial bundles differentiates in a wavelike continuum; meristematic regions precede the acropetally developing procambial bundles, (3) discrete subsidiary bundles differentiate in the meristematic regions as they advance acropetally, (4) subsidiary bundles diverge obliquely in the lamina margin giving rise to the secondary veins in a basipetal fashion, and (5) subsequent differentiation and maturation of the secondary veins occurs within the lamina. The original procambial bundles and first-formed subsidiary bundles become the secondary veins of the uppermost portions of the lamina, the next-formed subsidiary bundles become the secondary veins of the middle portions of the lamina, and the last-formed subsidiary bundles become the secondary veins of the lowermost portion of the lamina.     

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.     

从幼苗形态学特征探讨红豆杉科各属间的系统演化

本文根据幼苗的形态学特征,尤其是子叶的结构、说明在红豆杉科中最原始的属是榧树属,其幼苗为留土萌发,植株粗壮;子叶肥厚,有吸收功能,叶肉不分化,其细胞中充满淀粉粒：维管束在子叶的上部或顶部为单束2条,下部合并成双束1条。其次是穗花杉属,幼苗为出土萌发,植株粗壮,下胚轴的下部肥厚;子叶稍肉质,叶肉不分化,质体淡绿,有一定的光合功能,但主要是积累淀粉,维管束双束1条,在子叶的顶端趋于分裂。最进化的是红豆杉属和白豆杉属,可能还有澳洲红豆杉属,其幼苗为出土萌发,植株纤细;子叶薄,叶状,叶肉分化成栅栏和海绵组织,维管束单束1条。本科中族的划分和属的系统排列,从原始到进化,应该是：族1．榧树族(1．榧树属);族2．穗花杉族(2．穗花杉属);族3．红豆杉族(3．澳洲红豆杉属,4．红豆杉属,5．白豆杉属)。     

THE VASCULAR SYSTEM OF THE INFLORESCENCE AXIS OF ANDROPOGON GERARDII (GRAMINEAE) AND ITS BEARING ON CONCEPTS OF MONOCOTYLEDON VASCULAR TISSUE

The vascular bundles in the inflorescence axis of Andropogon gerardii occur in inner and outer systems. The inner system is made up of large, early developing strands that, at earliest stages of development, are precocious (= the appendage they are to serve has not yet been initiated). The outer system consists of later developing smaller strands that are open ended in a proximal direction (= strands differentiate basipetally in the cortex below the appendage they serve). Bundles of both the inner and outer systems are not connected to other procambium early in their development but exist as isolated strands. The veins of the inner system of the inflorescence axis occur as sympodia. The presence of inner and outer systems in the vascular tissue is common to most monocotyledons. However, amongst monocotyledons, only certain grasses have been shown to have strands of the inner system that are isolated early in development. Many dicotyledons have large strands which are precocious and some have smaller, later developing strands which are open ended in a proximal direction, hence they occur as isolated strands. These smaller strands in dicotyledons occur between large strands. Certain dicotyledons have an inner and an outer system of veins. Of these, some have veins of the inner system that differ from the inner system bundles of monocotyledons in that they also form part of the outer system of veins, or develop at a different time. One other dicotyledon with an inner and outer system, Bougainvillea, differs from monocotyledons only in that the bundles of the outer system do not seem to be isolated early in their development and anastomoses are seen between the inner and outer systems. Thus, it appears that monocotyledons differ from dicotyledons only in the presence of independent inner and outer systems of vascular bundles in the former. Thus, the hypothesis of Zimmermann and Tomlinson that there are basic differences between monocotyledon and dicotyledon vascular systems is not substantiated. It is even suspected that monocotyledon and dicotyledon vascular systems will be demonstrated to be modifications of a basic plan consisting of large, acropetally differentiating and smaller, basipetally differentiating strands.     

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.     

双子叶植物出土幼苗根茎转变区维管组织发育动态

关于根茎初生维管系统之间的连接以及与子叶的关系,在文献中已有广泛的论述,有过各种不同的解释。大部分早期关于根茎转变区的文献研究的是初生组织已完成发育的幼苗。这些研究者认为转变区域是根和茎这两种轴器官之间维管组织发生转变、相互连接的区域。但由于茎中的初生维管组织可以认为是叶迹及叶迹的延伸的综合,转变区域应被看作是轴维管系统与叶迹维管系统之间的连接。因此,转变区的研究必须说明根维管系统与最早的真叶叶迹之间的关系。通过对北乌头和大豆胚胎及幼苗维管组织的解剖学研究,本工作显示在出土萌发的双子叶植物中,初生维管组织在根-下胚轴-子叶中形成一连续系统,并完成根与子叶叶迹之间的维管组织过渡转变。而上胚轴中的维管组织是位于根-下胚轴-子叶上方独立形成的第二维管系统。上胚轴中维管组织的分化起始于第一真叶叶迹基部,向上分化进入叶片,向下进入胚轴并在子叶节下方与根-下胚轴-子叶维管系统相连接。真叶叶迹的木质部与下胚轴中靠近韧皮部的后生木质部或次生木质部连接。根与上胚轴之间不存在维管组织的过渡、转变,而只是在同样发育方向的组织中有一种直接的简单的连接．     

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.     

伊贝母种子萌发和籽苗建立

在子叶出土萌发的植物类型中,伊贝母种子萌发过程是罕见的。萌发初期,子叶优先生长。首先伸长而突破种皮,接着长出地面,此后,胚根才开始生长并产生不定根。种子萌发后形成特殊籽苗。在地上部分,子叶变绿,成为第一生长季唯一的同化叶;在地下部分,上胚轴扁平化,芽鳞肉质化,于是形成小鳞茎。籽苗形态属于最简化的类型。伊贝母的籽苗与其营养更新苗相比,是很弱小的。     

浙江淡水维管束植物的区系特点与地理分布

根据15年的调查结果,对浙江省水生维管束植物的区系与地理分布特点进行了研究。已知浙江有水生维管束植物150种,隶属于78属,42科。将78属归纳为11个分布区类型,以世界分布类型所占比例最高,热带分布属总数多于温带分布属,泛热带分布和北温带分布比例非常高。将150种植物归纳为13个分布区类型,温带分布远多于热带分布,以东亚分布类型最为突出,体现了中国－日本植物区系的明显特征,探讨了浙江水生植物的水平地带性和垂直地带性分布规律,其分布不仅与气候带有关,更与水生的生境的分布格局有关。最后,报浙江水生植物濒危种的受威胁状况。     

Granitic and gneissic outcrops (inselbergs) as centers of diversity for desiccation-tolerant vascular plants

Although desiccation tolerance is common in non-vascular plants, this adaptive trait is very rare in vascular plants. Desiccation-tolerant vascular plants occur particularly on rock outcrops in the tropics and to a lesser extent in temperate zones. They are found from sea level up to 2800 m. The diversity of desiccation-tolerant species as measured by number of species is highest in East Africa, Madagascar and Brazil, where granitic and gneissic outcrops, or inselbergs, are their main habitat. Inselbergs frequently occur as isolated monoliths characterized by extreme environmental conditions (i.e., edaphic dryness, high degrees of insolation). On tropical inselbergs, desiccation-tolerant monocotyledons (i.e., Cyperaceae and Velloziaceae) dominate in mat-like communities which cover even steep slopes. Mat-forming desiccation-tolerant species may attain considerable age (hundreds of years) and size (several m in height, for pseudostemmed species). Both homoiochlorophyllous and poikilochlorophyllous species occur. In their natural habitats, both groups survive dry periods of several months and regain their photosynthetic activity within a few days after rainfall. Other desiccation-tolerant species colonize shallow depressions, crevices and even temporarily water-filled rock pools on inselbergs. Desiccation-tolerant vascular plants occur in 13 families and are best represented within the monocotyledons and ferns. Only a few desiccation-tolerant dicots exist, in the Gesneriaceae, Myrothamnaceae and Scrophulariaceae. In total, about 330 species of vascular desiccation-tolerant plants are known, of which nearly 90% occur on inselbergs. With regard to morphological adaptations, the mat-forming monocotyledons are particularly remarkable due to the possession of roots with a velamen radicum, which is reported here in the genus Borya for the first time.     

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.     

Histochemical studies on protease formation in the cotyledons of germinating bean seeds

Summary Protease formation in Phaseolus vulgaris L. cotyledons during seed germination was studied histochemically using a gelatin-film-substrate method. Protease activity can be detected by this method on the 5th day of germination, at approximately the same time that a rapid increase of activity was observed by a test-tube assay with casein as a substrate. At the early stage of germination, protease activity was observed throughout the cotyledon except in two or three cell layers below the cotyledon surface and in several cell layers around the vascular bundles. A highly active cell layer surrounding the protease-inactive cells near the vascular bundles is suggested to be a source of the protease.Brooklyn Botanic Garden Contribution No. 202.     

Leaf anatomy of the Menispermaceae tribe Tiliacoreae Miers

WILKINSON, H. P., 1988. Leaf anatomy of the Menispermaceae tribe Tiliacoreae Miers . An anatomical study of the leaves of 25 species belonging to 12 of the 19 genera has been made. The anatomical characters found to be of the most use in distinguishing taxa or groups of taxa are: in surface view–stomatal outline, stomatal density and distribution, subsidiary cell or surrounding cell patterns, presence /absence of hairs; in transverse sections–dimensions of adaxial epidermal cells, morphology of spongy mesophyll, midrib outline, number and distribution of vascular bundles, presence/absence of an upper pulvinus, presence/absence of sclereids in the upper pulvinus, presence/absence of secretory sacs, crystal type and distribution.     

ABNORMAL GUARD CELL DEVELOPMENT IN AN OLIVE NECROTIC MUTANT OF MAIZE

A study of a mutant variety of Zea mays (ON8147) revealed that the mutant plants, in contrast with normal maize plants, do not exhibit a light-induced increase in the rate of transpiration, and that the ontogeny of the stomatal complex is abnormal. In later stages of differentiation, the guard cells of mutant plants deteriorate, leaving the mature stomata with only the two subsidiary cells. The subsidiary cells in stomata of mutant leaves are similar to those of normal leaves with respect to their capacity to accumulate K⁺ in the dark, but they do not lose K⁺ in the light, as do subsidiary cells of stomata of nonmutant plants. It is suggested that impairment of guard cell function causes death of the mutant plant seedlings primarily by restricting CO₂ entry into the leaf.     

THE OCCURRENCE OF INTERCALARY AND UNINTERRUPTED MERISTEMS IN THE INTERNODES OF TROPICAL MONOCOTYLEDONS

The distribution of percent of dividing nuclei, parenchyma cell length, total cell number per internode, and total internode length were determined for successive internodes in the apex and growing vegetative internodes of 23 tropical species in 17 families of monocotyledons. Basal intercalary meristems (IM) were found in representatives of Commelinaceae, Cyperaceae, Flagellariaceae, Poaceae, Restionaceae, and Marantaceae. Uninterrupted meristems (UM) which are confined progressively to the upper region of the internode and are not isolated meristematic regions were found in the Costaceae, Dioscoreaceae, Philesiaceae, Smilacaceae, Agavaceae, Araceae, Arecaceae, Liliaceae, Pandanaceae, and Zingiberaceae. Both IM and UM were found in different species of Orchidaceae. The only morphological trait correlated with meristem type was presence of sheathing leaf bases in all species with IM. Both IM and UM are interpreted as extensions of the primary elongating meristem; the IM is disjunct, and the UM is continuous with it. The phytomer growth unit and the presence of internodal IM's cannot be applied generally to the monocotyledons.     

COMPARATIVE STUDY OF THE FLORAL VASCULATURE IN SAURURACEAE

The floral vascular systems are compared among all six taxa of Saururaceae, including the two species of Gymnotheca which have not been studied previously. All are zygomorphic (dorsiventrally symmetrical), not radial as sometimes reported, in conformity with dorsiventral symmetry during organogenesis. Apocarpy in the two species of Saururus (with four carpels and six free stamens) is accompanied by a vascular system of four sympodia, each of which supplies a dorsal carpellary bundle, two ventral carpellary bundles, and one or two stamen traces. The level at which the ventral bundles diverge is the major difference in vasculature between the two species. The other four taxa are all syncarpous, and share some degree of stamen adnation and/or connation. The vascular systems also show varying degrees of fusion. The two species of Gymnotheca (with four carpels and six stamens) are very similar to each other; in both, the ventral traces of adjacent carpels fuse to form a placental bundle, which supplies the ovules and then splits into a pair of ventral strands. The flowers of Houttuynia cordata (with only three carpels and three adnate stamens) are sessile. Each flower is vascularized by three sympodia; the median adaxial sympodium is longer than the other two sympodia before it diverges to supply the adaxial organs. Three placental bundles also are formed in Houttuynia, but the three bundles differ in their origin. The median abaxial placental bundle diverges at the same level as the three sympodial bundles of the flower, while the other two lateral placental bundles diverge at a higher level from the median adaxial sympodium. Anemopsis californica, with an inferior ovary of three carpels, sunken in the inflorescence axis, and six stamens adnate to the carpels, has a vascular system very similar to that of Houttuynia cordata. The modular theory of floral evolution is criticized, on the bases of the known behavior of apical meristems and properties of vascular systems. The hypothesis is supported that saururaceous plants may represent a line of angiosperms which diverged very early.     

THE OCCURRENCE AND DISTRIBUTION OF ACRASIEAE IN FORESTS OF SUBTROPICAL AND TROPICAL AMERICA

Forests of the subtropical and tropical regions of North America harbor cellular slime molds not found in the soils of temperate deciduous forests investigated previously. However, most species found in the temperate forest are common in the tropics. Although the diversity of forms is greater in the soils of tropical forests the numbers of Acrasieae per unit of soil are comparable. Characteristic of tropical and subtropical forest soils are Acrasieae bearing crampon bases, of which four new species of Dictyostelium are presently known. Also present, but less frequently isolated, are two other new species of the genus Dictyostelium and two still undescribed species of the Guttulinaceae. Occasional isolates of D. purpureum and D. discoideum were found that produce macrocysts, which seem, also, to be confined to tropical and subtropical areas. Macro-cysts were previously known only in D. mucoroides and D. minutum isolated from temperate forest soils. The occurrence and distribution of Acrasieae in warm temperate desert and mesquite-scrub, in subtropical hammock, and in tropical thorn, deciduous, seasonal evergreen, rain, and cloud forests were investigated. Acrasieae were well represented in all of these forests except desert. The number of species and the total populations were largest in seasonal evergreen forests. The composition of the cellular slime mold populations and the dominant species within these populations could be related to the soil environment as expressed by the dominant vegetation.     

Limited evolutionary divergence of seedlings after the domestication of plant species

The most vulnerable stage in the life of plants is the seedling. The transition from wild to agricultural land that plants experienced during and after domestication implied a noticeable change in the seedlings′ environment. Building on current knowledge of seedling ecology, and on previous studies of cassava, we hypothesise that cultivation should have promoted epigeal germination of seedlings, and more exposed and photosynthetic cotyledons. To test this hypothesis, we phenotyped seedling morpho‐functional traits in a set of domesticated and wild progenitor accessions of 20 Eudicot herbaceous crop species. Qualitative traits like epi‐ versus hypogeal germination, leafy versus storage type of cotyledons, or crypto‐ versus phanerocotyledonar germination, remained conserved during the domestication of all 20 species. Lengths of hypocotyls and epicotyls, of cotyledon petioles, and indices of cotyledon exposure to the aboveground environment changed during evolution under cultivation. However, those changes occurred in diverse directions, depending on the crop species. No common seedling phenotypic convergence in response to domestication was thus detected among the group of species studied here. Also, none of the 20 crops evolved in accordance with our initial hypothesis. Our results reject the idea that strong selective filters exerted unconsciously by artificial selection should have resulted in generalised channelling of seedling morphology towards more productive and more herbivore risky phenotypes. This result opens up unexplored opportunities for directional breeding of seedling traits.