STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. I. ANTARCTICYCAS,GEN. NOV., A TRIASSIC CYCAD STEM FROM THE BEARDMORE GLACIER AREA

Silicified stems with typical cycadalean anatomy are described from specimens collected from the Fremouw Formation (Triassic) in the Transantarctic Mountains of Antarctica. Axes are slender with a large parenchymatous pith and cortex separated by a narrow ring of vascular tissue. Mucilage canals are present in both pith and cortex. Vascular tissue consists of endarch primary xylem, a narrow band of secondary xylem tracheids, cambial zone, and region of secondary phloem. Vascular bundles contain uni- to triseriate rays with larger rays up to 2 mm wide separating the individual bundles. Pitting on primary xylem elements ranges from helical to scalariform; secondary xylem tracheids exhibit alternate circular bordered pits. Traces, often accompanied by a mucilage canal, extend out through the large rays into the cortex where some assume a girdling configuration. A zone of periderm is present at the periphery of the stem. Large and small roots are attached to the stem and are conspicuous in the surrounding matrix. The anatomy of the Antarctic cycad is compared with that of other fossil and extant cycadalean stems.     

PHLOEM OF SPHENOPHYLLUM

The phloem of most fossil plants, including that of Sphenophyllum, is very poorly known. Sphenophyllum was a relatively small type of fossil arthrophyte with jointed stems bearing whorls of leaves ranging in form from wedge or fan-shaped to bifid, to linear. The aerial stem systems of the plant exhibited determinate growth involving progressive reduction in the dimensions of the stem primary bodies, fewer leaves per whorl, and smaller and simpler leaves distally. The primary phloem occurs in three areas alternating in position with the arms of the triarch centrally placed primary xylem. Cells of the primary phloem, presumably sieve elements, are axially elongate with horizontal to slightly tapered end walls. In larger stems with abundant secondary xylem and secondary cortex or periderm, a zone of secondary phloem occurs whose structure varies in the three areas opposite the arms of the primary xylem, as opposed to the three areas lying opposite the concave sides of the primary xylem. The axial system of the secondary phloem consists of vertical series of sieve elements with horizontal end walls. In the areas opposite the protoxylem the parenchyma is present as a prominent ray system showing dilation peripherally. Sieve elements in the areas opposite the protoxylem arms have relatively small diameters. In the areas between the protoxylem poles the secondary phloem sieve elements have large diameters and are less obviously in radial files, while the parenchyma resembles that of the secondary xylem in these areas in that it consists of strands of cells extending both radially and tangentially. An actively meristematic vascular cambium has not been found, indicating that this layer changed histologically after the cessation of growth in the determinate aerial stem systems and was replaced by a post-meristematic parenchyma sheath made up of axially elongate parenchyma lacking cells indicative of being either fusiform or ray initials. A phellogen arose early in development in a tissue believed to represent pericycle and produced tissue comparable to phellem externally. Normally, derivatives of the phellogen underwent one division prior to the maturation of the cells. Concentric bands of cells with dark contents apparently represent secretory tissue in the periderm and cell arrangements indicate that a single persistent phellogen was present. Sphenophyllum is compared with other arthrophytes as to phloem structure and is at present the best documented example of a plant with a functionally bifacial vascular cambium in any exclusively non-seed group of vascular plants.     

白鲜营养器官解剖结构及其与白鲜碱的积累关系

应用植物解剖学、组织化学及植物化学方法对白鲜营养器官根、茎、叶的结构及其生物碱的积累进行了研究。结果显示:(1)白鲜根的次生结构以及茎和叶的结构类似一般双子叶植物;白鲜多年生根主要由周皮、次生韧皮部、维管形成层以及次生木质部组成,根次生韧皮部中可见大量的淀粉、草酸钙簇晶、韧皮纤维以及油细胞;茎由表皮、皮层、维管组织和髓组成;叶由表皮、栅栏组织、海绵组织和叶脉组成;在茎和叶初生韧皮部的位置均分布有韧皮纤维,在叶表皮上分布有头状腺毛和非腺毛;在茎和叶紧贴表皮处分布有分泌囊。(2)组织化学分析结果显示:在白鲜多年生根中,生物碱类物质主要分布在周皮、次生韧皮部、维管形成层和木薄壁细胞中;在茎中,生物碱主要分布在表皮、皮层、韧皮部、木薄壁细胞及髓周围薄壁细胞中;在叶中,生物碱主要分布在表皮细胞、叶肉组织和维管组织的薄壁细胞;此外在分泌囊和头状腺毛中亦含有生物碱类物质。(3)植物化学结果显示,秦岭产白鲜根皮/白鲜皮、根木质部、茎和叶中白鲜碱含量分别为0.041%、0.012%、0.004%和0.002%,其中木质部中白鲜碱含量和其他部分地区白鲜皮中白鲜碱含量类似。研究表明,在秦岭产白鲜营养器官中,除根皮/白鲜皮外,在根木质部亦含有大量的白鲜碱,且在茎和叶中亦含有一定的白鲜碱,具有潜在的开发利用价值。     

A WOODY LYCOPSID STEM FROM THE NEW ALBANY SHALE (LOWER MISSISSIPPIAN) OF KENTUCKY

A lycopsid axis from the New Albany Shale (Sanderson Formation) of Kentucky is described. The stem, which branches dichotomously, is 45 mm in diameter and is characterized by a relatively narrow parenchymatized protostele, a 3.0 mm-thick cylinder of secondary xylem, a tripartite cortex, and a periderm that is more than 5.0 mm thick. The secondary xylem is composed of uniseriate and biseriate vascular rays and narrow tracheids with scalariform wall thickenings on both radial and tangential walls. The periderm is characterized by elongate, thick-walled cells, some of which broaden tangentially in the outer part of the tissue forming zones that appear wedge-shaped in cross section. Surface features of the axis, including leaf bases, are not preserved. The stem is tentatively regarded as a member of the Lepidodendrales in accordance with the numerous anatomical characters that it shares with more recent representatives of the order. Because the external morphology is not known, however, the possibility exists that the axis corresponds to a protolepidodendralean taxon currently known only from compression and/or impression remains or some other nonlepidodendralean plant that produced secondary xylem. The extremely narrow profile of the secondary xylem tracheids (relative to other arborescent lycopsids) is interpreted as evidence that the plants grew in a habitat that was substantially drier than the Upper Carboniferous coal swamps.     

西洋参根的发育解剖学研究

西洋主根顶端的原分生组织由三群原始细胞组成。初生木质部为三原型。维管形成层产生的次生维管组织中薄壁细胞占主导地位;维管分子量少、聚集成群,分散在薄壁组织中。周皮加、周皮发生较迟,其木栓形成层由紧靠内皮层的皮层细胞产生。不同年龄西洋参主根随着龄龄的增加,周皮、次生真心皮部和木质部面积均呈增加趋势,但韧皮部与木质部面积比值自５：１下降至１：１。一年生根由中柱鞘产生初生分泌道,由维管形成层产生一圈次生分     

远志根的发育解剖学研究

运用石蜡切片法对远志根的发育过程及1~3年生根的结构进行解剖学研究。结果显示:远志根的原分生组织由3群原始细胞组成,具有典型分生组织的细胞学特征。初生分生组织分化为根冠原、表皮原、皮层原和中柱原;初生结构由表皮、皮层和中柱组成,初生木质部为二原型。次生生长是依靠维管形成层和木栓形成层的活动完成,次生结构从外到内由周皮和次生维管组织组成;远志根次生结构特点为:次生韧皮部在次生维管组织中占主要部分,次生韧皮部中以韧皮薄壁细胞为主且其中储存有丰富的内含物,随着根龄的增加,韧皮薄壁细胞中的内含物也随之增加。3年生的主根中次生韧皮部薄壁细胞中的内含物最丰富;不同年份远志的主根随根龄的增加,周皮、次生韧皮部和次生木质部的面积都呈增加趋势,其中韧皮部和木质部的面积比值随根龄增长呈由小到大的变化,这是远志根的显著特点;根中的周皮发达,具有较厚的木栓层,次生木质部中导管和纤维发达,导管分布频率较高,并具有较大的口径。周皮和次生木质部的结构特征与远志的抗旱特性相适应。     

QUAESTORA AMPLECTA GEN. ET SP. N., A STRUCTURALLY SIMPLE MEDULLOSAN STEM FROM THE UPPER MISSISSIPPIAN OF ARKANSAS

A well preserved, permineralized seed fern stem is described from the Upper Mississippian Fayetteville Formation of north central Arkansas. Quaestora amplecta gen. et sp. n. is 41.6 cm long and exhibits six pairs of decussate, highly decurrent petiole bases. The stem has a cruciform, exarch protostele with prominent secondary xylem, vascular cambium and secondary phloem. Leaf traces are terete and occur as an outer ring with a small number of internal strands. The cauline vasculature, leaf-trace production, petiolar anatomy and several other features indicate that this specimen represents the most structurally simple and geologically ancient medullosan stem presently recognized.     

Empirical Models for Xylogenesis in Populus deltoides

Empirical quantitative models were constructed for Populus deltoidesdescribing temporal and spatial changes in vessel characteristicsof metaxylem, both within individual central leaf traces andwithin all central leaf traces considered as a morphologicalunit at a given transverse level in the stem (the central tracesympodia). Similar models were constructed for secondary vesselcharacteristics. The growth processes of the stem segment throughwhich the vasculature extended were incorporated in these modelsto illustrate how a functional vascular system is maintainedin the stem as a whole. The central trace sympodia representedthe integrals of the temporal and spatial functions for individualcentral leaf traces. Metaxylem vessel production ceased in individualleaf traces two plastochrons before the cessation was reflectedin the central trace sympodia because of the integrative natureof the sympodial complex. A functional continuum of developmentwas apparent between metaxylem vessels of the central tracesympodia and secondary vessels of the stem. The transition betweenmetaxylem and secondary xylem production in the central tracesympodia corresponded with cessation of leaf and internode elongation. Populus deltoides Bartr. ex Marsh., cottonwood, primary xylem, secondary xylem, primary-secondary vascular transition, leaf growth, xylogenesis     

桔梗根的发育解剖学研究

以桔梗(Platycodon grandiflorum A.DC)根为材料,运用石蜡切片和半薄切片法对其根的发育过程及结构进行解剖学观察,并对不同年限根的结构进行了比较。结果表明:桔梗根的结构发育过程包括原生分生组织、初生分生组织、初生生长和次生生长4个阶段。其原生分生组织由3群原始细胞组成,表现出典型分生组织的细胞学特征;初生分生组织包括根冠原、表皮原、皮层原和中柱原;初生结构由表皮、皮层和中柱组成,其中皮层薄壁细胞占主要地位,初生木质部为二原型;次生生长主要依靠维管形成层和木栓形成层的活动来完成,其次生结构从外到内由周皮和次生维管组织组成,次生维管组织占主导地位,其中以薄壁细胞为主,维管分子少量,分散在薄壁组织中。不同年限的根的结构基本相同,但它们在主根长度和直径、周皮厚度、木质部与韧皮部面积之比等方面存在差异。     

CAULINE VASCULATURE AND LEAF TRACE PRODUCTION IN MEDULLOSAN PTERIDOSPERMS

Medullosa and Sutcliffia specimens from the Paleozoic of North America and Europe are examined to determine the architecture of the cauline vasculature and mode of leaf trace production. Emphasis is placed on the identification and characterization of protoxylem strands and their relationship to leaf trace production. Organization of the primary xylem varies from a single protostele to a dissected stele composed of two to many more or less independent bundles. In Medullosa the bundles of primary xylem are each surrounded by secondary xylem, forming separate segments of vascular tissue (‘steles’ of previous workers). These vascular segments may divide and fuse at different levels in the stem. A definite number of protoxylem strands occur near the periphery of the primary xylem. The protoxylem strands divide at intervals producing protoxylem to the departing leaf traces. Leaf traces thus formed arise from all the vascular segments in a coordinated and predictable way and pass outward through emission areas in the secondary xylem. This type of cauline vascular architecture is compared to that of other seed plants. The vascular system of Medullosa stems is interpreted as a dissected monostele. Sympodial vascular architecture has apparently evolved from a protostele separately within the medullosan pteridosperms.     

Observations on phyllotaxis, stelar morphology, the shoot apex and gemmae of Lycopodium lucidulum Michaux (Lycopodiaceae)

Phyllotaxis in Lycopodium lucidulum consists of low alternating spirals, with the adult shoots corresponding to a system of 5 + 5 contact parastichies in which there are ten orthostichies. Each major stelar lobe is a sympodium of the leaf traces of two orthostichies and each lobe has two mesarch xylem poles, Differentiation of both the procambium and xylem of the leaf traces is bidirectional, that is differentiation first commences in the leaf base and then is acropetal into the leaf and basipetal into the stem. Furthermore, the procambium of the axis does not extend above that of the youngest leaf primordium and the axial procambium is in part a composite of that of the leaf traces. Thus, it is concluded that the stele in this taxon is not a strictly cauline structure. The shoot apex consists of four zones—a zone of surface initials, a zone of subsurface initials, a peripheral zone and a rib meristem. This zonation pattern is essentially the same as that of the seed plants. From their inception, gemma primordia also exhibit shoot apical zonation and are entirely different from leaves in their subsequent growth pattern and vascularization. Although the gemmae occupy leaf sites in the phyllotactic sequence, they are interpreted as arrested stem dichotomies on the basis of their development and vascular system.     

Ashicaulis woolfei n. sp.: additional evidence for the antiquity of osmundaceous ferns from the Triassic of Antarctica

Numerous small fern trunks and dispersed osmundaceous frond fragments occur within a Middle Triassic silicified peat near Fremouw Peak in the Transantarctic Mountains of Antarctica. These specimens form the basis of a new species of osmundaceous ferns that further helps to characterize the early Mesozoic vegetation of high latitude Gondwana. Ashicaulis woolfei n. sp. consists of small, upright trunks with a persistent armor of frond bases, adventitious roots, and vegetative frond parts. In cross section the trunks are ～2.5 cm in diameter and include up to 45 frond bases. Stems range from 5 to 8 mm in diameter with a xylem cylinder of 8-9 xylem segments separated by leaf gaps. Phyllotaxy is variable, approaching 2/5 or 3/8, with 10-12 frond traces in the cortex. Stipes have parenchymatous, stipular wings that are usually devoid of sclerenchyma; fronds are pinnate with alternate-subopposite pinnatifid pinnules. Although the absence of fertile pinnules and sporangia precludes assigning the fossils to a living genus, this species demonstrates that ferns with stelar architecture and histology similar to Osmunda subgenus Osmundastrum (Osmundaceae) were present in the Southern Hemisphere by the mid-Triassic.     

THE RELATIONSHIP BETWEEN THE PRIMARY THICKENING MERISTEM AND THE SECONDARY THICKENING MERISTEM IN YUCCA WHIPPLEI TORR. I. HISTOLOGY OF THE MATURE VEGETATIVE STEM

Anatomical observations were made on 1-, 2-, and 3-yr-old plants of Yucca whipplei Torr, ssp. percursa Haines grown from seed collected from a single parent in Refugio Canyon, Santa Barbara, California. The primary body of the vegetative stem consists of cortex and central cylinder with a central pith. Parenchyma cells in the ground tissue are arranged in anticlinal cell files continuous from beneath the leaf bases, through the cortex and central cylinder to the pith. Individual vascular bundles in the primary body have a collateral arrangement of xylem and phloem. The parenchyma cells of the ground tissue of the secondary body are also arranged in files continuous with those of the primary parenchyma. Secondary vascular bundles have an amphivasal arrangement and an undulating path with frequent anastomoses. Primary and secondary vascular bundles are longitudinally continuous. The primary thickening meristem (PTM) is longitudinally continuous with the secondary thickening meristem (STM). Axillary buds initiated during primary growth were observed in the leaf axils. The STM becomes more active prior to and during root initiation. Layers of secondary vascular bundles are associated with root formation.     

ANATOMICALLY PRESERVED GLOSSOPTERIS STEMS WITH ATTACHED LEAVES FROM THE CENTRAL TRANSANTARCTIC MOUNTAINS,ANTARCTICA

Stems and buds of Glossopteris skaarensis Pigg and buds of G. schopfii Pigg from the Permian Skaar Ridge locality in the central Transantarctic Mountains, Antarctica demonstrate the first anatomically preserved glossopterids known with stem/leaf attachment. Stems of G. skaarensis are 1–12 mm in diameter ( = 3.1 mm) with a broad pith, poorly defined primary xylem, and a zone of secondary xylem up to 6 mm thick. Pycnoxylic wood conforming to Araucarioxylon Kraus is composed of tracheids with uni- to biseriate oval to hexagonal bordered pits on radial walls, uniseriate rays one to a few cells high, and cupressoid to taxodioid cross-field pitting. Stems have a narrow zone of secondary phloem, aerenchymatous cortex with scattered sclereids, and sometimes a narrow periderm. Two wedge-shaped leaf traces each bifurcate to form four strands in the base of each petiole. Small axillary branches are vascularized by double branch traces that fuse at the margin of the main axis. Buds of G. skaarensis have leaves with narrow lateral laminae and a thickened midrib containing a wide lacuna, delicate vascular strands, and a prominent hypodermis. In contrast, buds of G. schopfii have uniformly thick leaves with prominent, circular vascular bundle sheaths. These anatomical details are used to reconstruct individual types of glossopterid plants, providing new information toward understanding the ecology and evolution of this important group of Permian seed plants.     

Developmental anatomy of vascular cambium and periderm ofBotrypus virginianus and its bearing on the systematic position of ophioglossaceae

The developmental anatomy of the vascular cambium and periderm ofBotrypus virginianus was studied, and its bearing on the systematic position of Ophioglossacease is discussed. The cambial zone including cambium is initiated in a procambial ring of the stem before primary vascular tissue is well differentiated. The presumed cambium is composed of fusiform and ray initials. The cambium is extremely unequally bifacial, producing secondary xylem centripetally, and quite a small number of parenchymatous cells but no secondary phloem centrifugally. The cambial activity persists long, although it is very low in the mature part of the stem. It seems that the circumferential increase of the cambium is accommodated by an increase in the number of cambial initials. Secondary xylem is nonstoried and composed of tracheids with circular-bordered pits with evenly thick pit membranes, and uniseriate or partly biseriate radial rays. It makes up the bulk of the stem xylem. Periderm is formed almost entirely around the stem, simultaneous with its increment due to the secondary xylem. The combination of these anatomical features of secondary tissue supports the idea that Ophioglossaceae are living progymnosperms.     

不同生长年份移山参根的比较解剖学研究

采用石蜡制片法、显微观察生长8年、12年和16年的移山参主根中部的组织结构,并以4年生栽培参(二马牙)和西洋参为对照进行比较分析。结果表明,移山参主根结构由周皮和次生维管组织组成。不同生长年份的移山参主根结构具有一定差异:随生长年份的增长,木栓层细胞体积变小,排列趋于紧密;栓内层草酸钙结晶越来越少;分泌道均为3轮,但平均口径逐渐减小;韧皮部外侧和木质部靠近根中央处的薄壁组织的裂隙逐渐增大;韧皮部与木质部的面积比则不断下降;12年、16年生移山参主根次生木质部中导管数量和层数明显多于8年生。PAS 反应表明淀粉粒含量在生长12年以后趋于稳定。表明通过观察移山参木质部与韧皮部的面积比和次生维管组织中木质部导管的数量及层数,可以初步判断移山参的生长年份。     

A re-investigation of Halle's Drepanophycus spinaeformis Göpp. from the Lower Devonian of Yunnan Province, southern China

New collections of microphyllous plants identical to those described by Halle almost 60 years ago and identified by him as Drepanophycus spinaeformis Göpp., 1852 have been made from the Emsian Xujiachong Formation, near Qujing City, eastern Yunnan Province. New information relates to orientation of leaves, epidermal and xylem anatomy, vegetative and fertile leafy shoots with roots and sporangia. The latter, dehiscing distally into two equal valves diat are elliptical to circular in face view, are attached directly to the stem by short stalks. They show no consistent relationship to leaves and are supplied by a separate vascular trace much wider than that to leaves. Detailed comparison is made with the cosmopolitan and stratigraphically long-ranging species D. spinaeformis. The Chinese specimens can be distinguished on leaf orientation, their anomocytic stomata and sporangial characters, although the latter remain conjectural in D. spinaeformis, and are therefore placed in a new species Drepanophycus qujingensis. Hypotheses relating to cooksonioids, zosterophylls and the origin of the lycopsids are reviewed and the phylogenetic position of the new taxon assessed. It is concluded that it has greatest affinity with Astewxylon mackiei, and that both exhibit the kind of fertile organization that might be anticipated in the ancestors of the lycopsids.     

Comparative Studies on Differentiation of Regenerated Tissue in Broussonetia papyrifera

This paper describes the differentiation process of regenerated tissue after ordinary girdling or after removal of a section of xylem from the stem, and the disparity in differentiation of the regenerated tissues after being differently treateds in Broussonetia papyrifera. After ordinary girdling for 3–4 weeks, new bark regenerated in the xylem. During the process of rind' formation, many specks of meristematic tissue were formed in the callus, from which vascular tissue clusters were developed. In addition, the new periderm appeared almost at the same time as the new vascular cambium was seen. When a section of xylem was removed from the stem, numerous calli developed rapidly on the inner surface of the bark. Meanwhile, the vascular cambium appeared in the immature phloem. Soon after, discontinued meristematic tissue bands also occurred in the callus. These meristematic tissues then connected with each other to form a concave oblate cambial ring which developed xylem inward and phloem outward. About 2–3 weeks later, the concave oblate trunk grew lengthwisely connecting with the upper anct lower portions of the normal stem. By then, the tree continued to grow. The inner surface tissue of the bark, after the xylem was removed, differentiated about one week earlier than the tissue on the surface of the xylem after girdling.     

A new genus of filicalean fern from the Lower Permian of China

Recent investigation on the Cathaysian flora of the Lower Permian Taiyuan Formation in Hebei Province, North China has led to the discovery of a new type of fern, Rastropteris pingquanensis gen. et sp. nov. Preserved as a permineralization, the stem, with a mantle of petiole bases and roots, shows a unique combination of anatomical characters. The vascular strand consists of a solid protostele with uniformly elongated tracheids and mesarch maturation of the xylem. In transverse section, the configuration of leaf trace xylem changes from reniform endarch to a tangentially elongated strand adaxially recurved at each end with several adaxial ridges. Stem and petiole cortex contains abundant sclerotic tissue with an interstitial tissue developed within the mantle of petiole bases and roots. A reinvestigation of Grammatopteris rigollotii , from the Permian of France, the type species of the genus allows interpretation of the latter as closer to Rastropteris than any other fern. Both taxa are provisionally reported to an incertae sedis group of filicalean ferns possibly involved in the origin of Osmundaceae.     

六盘山鸡爪大黄蒽醌类化合物积累特征的研究

采用多种组织化学方法研究了六盘山鸡爪大黄营养器官中蒽醌类化合物的积累特征.结果显示:蒽醌类化合物在根中分布于周皮的木栓层和栓内层、次生维管组织的维管射线和根中央的部分木薄壁细胞内,且维管射线是根中贮藏和积累蒽醌类化合物的主要组织;在根茎中分布于周皮的木栓层和栓内层、次生维管组织的形成层和维管射线,以及髓的异常维管束射线中,且维管射线是根茎中贮藏和积累蒽醌类化合物的主要组织;在茎中主要分布于表皮、近表皮皮层和维管束的维管束鞘及其薄壁细胞,大型和小型维管束之间和周围的部分薄壁细胞,以及髓射线中有不同程度的分布;在叶中主要积累在叶柄的表皮、叶柄和大叶脉的部分基本组织、维管束的部分薄壁细胞等部位.结果表明,六盘山鸡爪大黄的根和根茎是蒽醌类化合物贮藏和积累的主要器官,维管射线是其贮藏和积累的主要组织,而且各营养器官中蒽醌类化合物积累的数量与植物各相关器官组织的发育程度、细胞中含淀粉粒的多少存在着一定的相关性.