Parenchymatous Ground Tissue Research Articles

Influence of structural reinforcements on the twist-to-bend ratio of plant axes: a case study on Carex pendula

During biological evolution, plants have developed a wide variety of body plans and concepts that enable them to adapt to changing environmental conditions. The trade-off between flexural and torsional rigidity is an important example of sometimes conflicting mechanical requirements, the adaptation to which can be quantified by the dimensionless twist-to-bend ratio. Our study considers the triangular flower stalk of Carex pendula, which shows the highest twist-to-bend ratios ever measured for herbaceous plant axes. For an in-depth understanding of this peak value, we have developed geometric models reflecting the 2D setting of triangular cross-sections comprised of a parenchymatous matrix with vascular bundles surrounded by an epidermis. We analysed the mathematical models (using finite elements) to measure the effect of either reinforcements of the epidermal tissue or fibre reinforcements such as collenchyma and sclerenchyma on the twist-to-bend ratio. The change from an epidermis to a covering tissue of corky periderm increases both the flexural and the torsional rigidity and decreases the twist-to-bend ratio. Furthermore, additional individual fibre reinforcement strands located in the periphery of the cross-section and embedded in a parenchymatous ground tissue lead to a strong increase of the flexural and a weaker increase of the torsional rigidity and thus resulted in a marked increase of the twist-to-bend ratio. Within the developed model, a reinforcement by 49 sclerenchyma fibre strands or 24 collenchyma fibre strands is optimal in order to achieve high twist-to-bend ratios. Dependent on the mechanical quality of the fibres, the twist-to-bend ratio of collenchyma-reinforced axes is noticeably smaller, with collenchyma having an elastic modulus that is approximately 20 times smaller than that of sclerenchyma. Based on our mathematical models, we can thus draw conclusions regarding the influence of mechanical requirements on the development of plant axis geometry, in particular the placement of reinforcements.

Anatomical adaptations and mycorrhizal morphology of two threatened Eulophia (Orchidaceae) growing in southern Western Ghats, India

The vegetative anatomy of Eulophia spectabilis (Dennst.) Suresh and Eulophia pulchra (Thouars) Lindl., of subfamily Epidendroideae (Orchidaceae), of subtribe Eulophiinae was investigated to bring out the anatomical differences, mycorrhizal morphology and also their adaptation to thrive in stressful xerophytic habitats. Transverse sections of plant parts were freehand sectioned and stained with various staining solutions for anatomical investigation. Stomatal characteristics were examined by maceration technique. The leaves of both Eulophia species shared similar anatomical characteristics including tertracytic stomata on abaxial surface, uniseriate epidermis on both the surfaces, homogenous mesophyll comprising of intercellular spaces and collateral vascular bundles. Fibre bundles are present only in the leaves of E. pulchra. Likewise, the anatomy of leaf-sheath in both the species resembles those of the leaves except for the large air chambers. The pseudobulb of E. pulchra consists of parenchymatous ground tissue containing air chambers, raphides, starch grains, and water-storage cells and collateral vascular bundles. Starch grains are present only in the rhizomes of E. pulchra ground tissues. In roots, the velamen is undifferentiated in E. pulchra, but distinguished into epivelamen and endovelamen in E. spectabilis. Starch grains are present in root pith cells in E. pulchra. The cell dimensions of most plant parts varied significantly (P<0.05) among the Eulophia species. Contrarily there were no significant (P>0.05) differences in orchid mycorrhizal colonization between the Eulophia species. Thus, these ground orchids possessed several anatomical features that enable them to thrive in dry habitats.

Microscopic Investigations and Pharmacognosy of Striga orobanchioides Benth

Objective: To study delineate Pharmacognosy of the stem of plant Striga Orobanchioides Benth (Scrophulariaceae), prime plant in Indian system of medicine. A comprehensive account on standardization of herbal drug Striga Orobanchioides Benth by using microscopic as well as Pharmacognostic parameters. In the field of herbal medicines, the main issues are quality, purity, and effectiveness, as in many cases herbal drugs are knowingly or unknowingly substituted or adulterated with similar species or varieties. Methods: The macroscopy, microscopy, physicochemical analysis, preliminary phytochemical testing of the powder of plant stem and other WHO recommended methods for standardization was done. Results: T S of young as well as old stem was studied. T.S. of the young stem confirmed the presence of thin epidermal layer, fairly wide cortex and thin vascular cylinder having the pith disintegrated or retained as homogeneous parenchymatous tissue. T.S. of the old stem confirmed the presence of cortical cells, parenchyma cells, sclerenchyma cells, vascular tissue. The lower conical part of the stem has epidermis cortical zone and vascular cylinder continued from its wide upper part. The cortical zone consists of parenchymatous ground tissue with sealed masses of sclerenchyma cells. The xylem tissue becomes gradually narrow and thin in the end of the stem. It includes compact radial lines of vessels, filnes and xylem rays. Conclusion: The above parameters, being reported to the first time for the studied plant species, and are significant towards establishing the microscopic and Pharmacognostic standards for future identification and authentication of genuine herbal drug. It can be concluded that the Pharmacognostic outline of Striga Orobanchioides plant is beneficial in developing standards for quality, purity and sample identification.

Date palm rachis as a raw material for wood composite industry: anatomical characteristics

This study is focused on the internal structure of leaf midrib (rachis) of some male tress of certain date palm cultivars, namely Khalas, Naboat-Saif, Sillej and Sukkary, common to Saudi Arabia. It takes into consideration the structure, dimension and abundance of vascular bundles (VBs), vessel lumen diameter, relative proportion of fibers and vessels in the vasculature at the basal and the middle parts along the length of the rachis. A large number of conjoint, collateral and closed VBs of varying sizes, embedded in the parenchymatous ground tissue, are normally present. The xylem in the VB often contains 6–15 protoxylem and 2–3 metaxylem vessels as seen in cross-sectional view. Vascular bundles have fiber caps, of which the upper ones were quite thicker than the lower (inner) ones in general. Cultivars Khalas and Sukkary are superior in having the highest midrib cross-sectional area (17.1 cm2 and 16.8 cm2, respectively). Moreover, Khalas have the highest fiber area fraction (17% and 25%), while Sukkary a highest vessel density (16–17 per VB) in both the basal and middle positions at the rachis. Cultivar Naboat-Saif is superior in having a high VB density (130 and 194 per cm2), narrowest vessels (42.4 µm and 53.5 µm) and thickest vessel wall (4.23 µm and 4.45 µm, respectively) both in the basal and in the middle position of the rachis length.

Comparative anatomy of Sirhookera (Orchidaceae) growing in Western Ghats of southern India

We compared the anatomical characteristics of vegetative organs, peduncle and mycorrhizal morphology of the two known species of Sirhookera (Epidendroideae, Orchidaceae) to identify anatomical markers for identification and the ecological adaptations of these species. The leaves are hypostomatic bearing tetracytic stomata and the walls of subsidiary cells are smooth in Sirhookera lanceolata and undulate in Sirhookera latifolia. On the adaxial and abaxial surfaces the leaves are covered by a thick cuticle. The hypodermis is dimorphic and present on both sides of the leaf; chlorenchyma is homogenous and the vascular bundles are collateral. The rhizome of Sirhookera possesses a single‐layered epidermis, thick cuticle, thin‐walled parenchymatous ground tissue containing starch grains and scattered collateral vascular bundles. A thick‐walled sclerenchymatous band separates the cortex from the parenchymatous ground tissue comprising of banded cells in the peduncle. Starch grains are present in the ground tissue of the S. latifolia peduncle. The roots consist of the velamen, ∩‐thickened exodermis, thin‐walled cortex consisting of water‐storage cells, O‐thickened endodermis and a vascular cylinder with parenchymatous pith. Starch grains are present in the root cortical cells of S. lanceolata but absent in S. latifolia. Fungal pelotons that aids in nutrient acquisition were observed in the root cortical region of both species. The study revealed significant differences between the anatomical characteristics of the two species and that most of the anatomical features of Sirhookera relate to their ecological adaptations.

Vegetative anatomy of the orchid Bulbophyllum sterile (Orchidaceae: Epidendroideae)

The anatomical characteristics of leaf, pseudobulb, and root of Bulbophyllum sterile of the subfamily Epidendroideae (Orchidaceae) were investigated. The anatomical investigation involved observing sections after staining with different stains as well as scanning electron microscopy. Additionally, the cell dimensions were also measured. The amphistomatic leaves of B. sterile had a thick cuticle, paracytic type of stomata, collateral vascular bundles and starch grains. The rhizome had cuticularized uniseriate epidermis and a single layer of the hypodermis. The parenchymatous stem ground tissue was distinguished into outer and inner regions separated by a band of sclerenchymatous tissue. Collateral vascular bundles were distributed in the inner ground tissue. The size of the vascular bundles generally increased from the periphery towards the center. A sclerenchymatous patch covered the phloem pole, whereas the xylem is covered by thin walled parenchymatous cells. The outer surface of the pseudobulb is covered by a thick cuticle. The parenchymatous ground tissue consisted of starch grains, aeration, water and algal cells and scattered collateral vascular bundles. Sclerenchymatous cells covered the phloem pole, whereas the xylem is covered by thin-walled cells. The velamen in B. sterile is single layered consisting of highly elongated compactly arranged cells. Uniseriate exodermis is dimorphic consisting of long and short cells. Cortical cells are differentiated into exodermis and endodermis. The O-thickened endodermal cell layer is interrupted by thin walled passage cells. Pith is sclerenchymatous. From this study, it can be concluded that B. sterile possess anatomical adaptations to xeric conditions in all the vegetative organs.

Vegetative anatomical adaptations of Epidendrum radicans (Epidendroideae, Orchidaceae) to epiphytic conditions of growth

The anatomical properties of leaf, stem, and root of Epidendrum radicans Pav. ex Lindl., belonging to the subfamily Epidendroideae (Orchidaceae) were investigated for adaptations to stressed habitats. The anatomical investigation revealed that leaves of E. radicans have a thick cuticle (3–4 µm) and paracytic type of stomata. Foliar epidermal cells are conical on the adaxial surface and rectangular in the abaxial surface, distinct hypodermis absent, and uniseriate fiber bundles are arranged in both sides of the leaves. The foliar mesophyll is homogenous and starch grains and raphides present. The leaf sheath covering the stem have cuticle restricted to the outer surface and air spaces are present. The stem has a cuticulerized uniseriate epidermis and a uniseriate hypodermis. The cortex and a parenchymatous ground tissue of the stem are separated by a layer of sclerenchymatous band. Vascular bundles are collateral and their size generally increases from the periphery towards the center. A sclerenchymatous patch covers the phloem pole, whereas the xylem is covered by thin-walled parenchymatous cells. The roots possess Epidendrum-type velamen. Cover cells present. Uniseriate dimorphic exodermis consists of U-thickened long cells and thin-walled passage cells. The endodermal cells O-thickened, pericycle sclerenchymatous, xylem 10–14 arched. The pith is sclerenchymatous, but parenchymatous at the center. The anatomical examination of E. radicans revealed adaptations to moisture stress conditions like thick cuticle covering the leaves and stem, water storage cells, multilayered velamen and dimorphic exodermis.

Cocowood Fibrovascular Tissue System-Another Wonder of Plant Evolution.

The coconut palm (Cocos nucifera L.) stem tissue (referred to as cocowood in this study) is a complex fibrovascular system that is made up of fibrovascular bundles embedded into a parenchymatous ground tissue. The complex configuration of fibrovascular bundles along with the non-uniform distribution of the material properties likely allow senile coconut stems to optimize their biomechanical performance per unit mass (i.e., mechanical efficiency) and grow into tall, slender, and very flexible plants with minimum resources of biomass and water. For the first time, to the best of the authors' knowledge, this paper examines, from the integral (i.e., stem structure) and macroscopic (i.e., tissue structure) levels of hierarchy, the characteristic triple helix formation depicted by the fibrovascular bundles within the monocotyledon cocowood. The natural course of the tangential orientation of the axial fibrovascular bundles is mapped for the whole cocowood structure by quantifying 264 cocowood discs, corresponding to 41 senile coconut palms estimated to be >70 years old. The observed variations were modeled in this paper by simple equations that partially enabled characterization of the cocowood fibrovascular tissue system. Furthermore, 11 finite element analyses (FEA) were performed over a three dimensional (3D) finite element (FE) model resembling a characteristic coconut palm stem of 25 m in height to analyze the biomaterial reactions produced by the progressive deviation of the tangential fibrovascular bundles on the cocowood mechanical response (i.e., on the material compressive strength and the bending stiffness). The analyses in this study were carried out for the critical wind speed of 23 m/s (i.e., Gale tornado according to the Fujita tornado scale). For each analysis, the characteristic average maxima degree of orientation of the cocowood fibrovascular bundles was varied from 0° to 51°. The acquired results provided a deep understanding of the cocowood optimum fibrovascular tissue system that denotes the natural evolution of the material through millions of years. The knowledge advanced from this study may also serve as concept generators for innovative biomimetic applications to improve current engineered wood products.

Study of the fungal decay of oil palm wood using TEM and UV techniques

Oil palm wood samples were subjected to decay by the brown-rot fungus Coniophora puteana and the white-rot species Pleurotus ostreatus. There was up to 61% mass loss by C. puteana and 32% by P. ostreatus within two month of incubation. Light microscopy of the decayed samples showed preferential degradation of the parenchymatous ground tissue and phloem in the vascular bundles. Transmission electron microscopy revealed details on the micromorphology of cell wall decay. C. puteana consumed the carbohydrates. P. ostreatus produced simultaneous white-rot. Ultraviolet microspectrophotometry provided insight in lignin degradation by P. ostreatus showing lignin decrease in the walls of parenchyma cells, fibers and vessels. C. puteana increased the UV absorbance due to depolymerization of the lignocelluloses matrix and modifications in the lignin side chains.

Morphology, anatomy and mycotrophy of pseudobulb and subterranean organs in Eulophia epidendraea and Malaxis acuminata (Epidendroideae, Orchidaceae)

The pseudobulbs and subterranean organs (roots and rhizomes) of Eulophia epidendraea, and Malaxis acuminata in subfamily Epidendroideae (Orchidaceae) were investigated to determine morphology, anatomy and mycorrhizal occurrence. The examined sections showed the following common anatomical characteristics. The pseudobulbs had a uniseriate epidermis. The assimilatory cells were scattered in the form of mucilage/water storage cells in the ground tissue. The vascular bundles were collateral and embedded in the ground tissue. Raphides occurred as idioblasts. Rhizomes had an uniseriate epidermis, parenchymatous ground tissue differentiated into outer and inner zones with polygonal intercellular spaces. Vascular bundles scattered, collateral and discontinuous form in both the taxa. Aeration cells were present in roots and rhizomes of M. acuminata. The transverse section of E. epidendraea roots had multi-layered velamen with spiral thickening followed by uniseriate exodermis with passage cells that had webbed tilosomes. The parenchymatous cortex contained raphides and water storage cells. Vascular bundles were 11–15 arched. Roots of M. acuminata had an uniseriate velamen, exodermis, parenchymatous cortex, endodermis and pericycle. The vascular bundles were radially arranged, and 11–12 arched. The xylem and phloem were embedded in sclerenchymatous tissue. The entry of the mycorrhizal fungi was chiefly through root hairs in roots and epidermis in rhizomes of M. acuminata, and in E. epidendraea. Fungi formed pelotons in both the taxa and microsclerotia and monilioid cells in the root cortex of E. epidendraea. Additionally, Glomus- type vesicles were occasionally present in the roots of M. acuminata. Description of characteristics arising from this investigation may provide additional morphological and anatomical means of identification.

Analysis of the hollow structure with functionally gradient materials of moso bamboo

Bamboo is a fiber-reinforced bio-composite with superior structural behavior. The hollow structure as well as the gradient distribution of bamboo fiber is the embodiment of the superior bamboo construction. To validate this, tensile tests were performed on bamboo test specimens. The volume fractions of bamboo fiber and parenchymatous ground tissue along the radius of the culm wall were scanned and calculated. The elastic moduli of bamboo fiber and parenchymatous ground tissue were estimated, according to the linear equations obtained by regression analysis. With the equivalent volume, a numerical hollow model and solid model were built to make comparative analysis on their mechanical behavior. For the purpose of verifying the advantage of fiber gradient distribution, models, which were composed of fiber and parenchymatous ground tissue with different fiber distributions, were built for comparative analysis. Results show that under the condition of using the same material, the hollow structure as well as fiber gradient distribution of bamboo possess excellent mechanical performance of bamboo structure.

Investigation into the deterioration process of archaeological bamboo strips of China from four different periods by chemical and anatomical analysis

The chemical and the anatomical features of the archeological bamboo strips of China from four different periods were compared with the non-degraded fresh bamboo to understand the deterioration process. Unprocessed bamboo strips, isolated hemicelluloses and lignin fractions were analyzed with wet chemical analysis, GC, FTIR, UV and XRD to investigate the chemical degradation. It was found that the crystalline cellulose and the polyxylose degraded with increasing age, leaving the amorphous cellulose and the lignin with syringyl moieties modified as the main residual cell wall materials. Serious degradation of p-coumaric acid and ferulic acid were detected and indicated the cleavage of the linkage between the lignin and the carbohydrate, which might facilitate the degradation of carbohydrate. The anatomical analysis with SEM and TEM revealed the vanishing of the parenchymatous ground tissue and vessels and the cellulose microfibrils in the multilayered secondary wall. The differences in lignin content and in tissue density (cell thickness/cell size) between the parenchyma cells and the sclerenchymatous fiber cells fundamentally led to the formation of the unique anatomical structure of the archeological bamboo strips which was composed of parallel solid bundles. The effects of the chemical and the anatomical degradation on the mechanical properties were also discussed.

Analysis of the Effects of Fiber Gradient Distribution on the Mechanical Properties of Moso Bamboo

Bamboo is a fiber-reinforced bio-composite with superior structural behavior. For the purpose of analyzing the correlations between the mechanical properties of bamboo and fiber volume fraction, tensile tests were performed on bamboo test specimen, and the corresponding volume fractions of fiber and parenchymatous ground tissue were measured. Linear and curvilinear regressions were done from tested data of elastic modulus, tensile strength and volume fractions of fiber. The results display that there is an obvious correlation between bamboo tensile properties and fiber volume fraction. In order to analyze the effects of fiber gradient distribution on bamboo structural behavior, models composed of fiber and parenchymatous tissue were built based on different fiber distribution for comparative analysis. The analysis results show that the maximum deformation of 4 layers model is 3.86% less than 1 layer model, and the maximum deformation of 8 layers model is 8.87% less than 4 layers model. In the part of maximum axial stress, the maximum axial stress of 4 layers model is 3.27% less than 1 layer model, and the maximum axial stress of 8 layers model is 8.90% less than 4 layers model. Conclusion can be drawn from the comparison that the strength and stiffness of the model appear to be growing with the degree of fiber gradient distribution deepening from 1 layer model to 4 layers model, and 4 layers model to 8 layers model.It can be concluded that the mechanical properties of bamboo structure are significantly improved because of fiber gradient distribution.

Removal of cationic and anionic azo dyes from aqueous solutions by adsorption on maize stem tissue

The present investigation reports an effective adsorption of both cationic and anionic azo dyes by maize stem parenchymatous ground tissue with the vascular bundles embedded in it (MSGT), as novel, inexpensive and abundantly available alternative to the other commercial adsorbents. The feasibility of MSGT, for the adsorptive removal of both cationic (Methylene blue – MB) and anionic (Eriochrome black T – EBT) dyes from aqueous solution was evaluated in a batch process. Kinetic of dyes adsorption followed the pseudo second-order equation (R2>0.997). The equilibrium data of both MB and EBT adsorption were well correlated by both Freundlich and Langmuir isotherm at initial dye concentration (20–50mg/L) and pH (2–6) ranges studied. Maximum Langmuir monolayer adsorption capacity of MSGT was found to be 160.84mg/g for MB at pH 6, and 167.01mg/g for EBT at pH 2. This study developed mathematical models for the optimization of pH, contact time and initial dye concentration for the adsorption of MB and EBT onto MSGT. Experimental values of the adsorption capacity were in good agreement with the optimum values predicted by the models.

Tensile properties of Moso bamboo (Phyllostachys pubescens) and its components with respect to its fiber-reinforced composite structure

Bamboo is a fiber-reinforced bio-composite since its culm wall is mainly composed of parenchymatous ground tissue in which vascular bundles are embedded. In order to analyze the mechanical properties of bamboo as a function of its components, tensile tests were performed on bamboo blocks and the corresponding volume fractions of fiber and parenchymatous ground tissue were measured. More significant linear relationships were found between tensile properties and volume fractions of the bamboo components. The tensile strength and modulus of elasticity of bamboo fiber and parenchymatous tissue were estimated according to the linear equations obtained by regression analysis. The macrographs of fractured bamboo blocks and the micrographs of fracture surfaces obtained by scanning electron microscope were also analyzed. Further tensile tests on separated bamboo fiber bundles were analyzed. Results show that the tensile strength of bamboo fiber obtained from the tests on bamboo blocks was higher than that on separated fiber bundles. This might be due to the interaction between components in bamboo in which parenchymatous ground tissue can pass loads and distribute the stresses loaded on fibers.

Anatomically Preserved Pteridosperm Stems and Rachises from Permian Floras of China

Pteridosperms are common in the Permian floras of China and are known from both vegetative and fertile organs in adpression assemblages and as dispersed ovules and seeds in permineralized assemblages. In contrast, reports of vegetative organs from permineralized assemblages are limited, and in all cases, accounts have not been verified by detailed descriptions nor illustration. Here we report four taxa of pteridosperm stem or rachis from the Permian permineralized floras of China. Coal balls from the Asselian‐Sakmarian (Cisuralian) Taiyuan Formation are shown to contain specimens of a medullosan and a lyginopterid pteridosperm. The medullosan rachis has a distinctive collateral organization of vascular bundles interspersed within a crushed parenchymatous ground tissue that also has scattered resin ducts, and it is identified as Myeloxylon Brongniart. The lyginopterid has a vitalized protostelic stem with manoxylic secondary xylem and mesarch xylem maturation and is confirmed as Heterangium sp. 1. From vol...

Stem anatomy of Dolichos lablab Linn (Fabaceae): Origin of cambium and reverse orientation of vascular bundles

Secondary growth in the stem of Dolichos lablab is achieved by the formation of eccentric successive rings of vascular bundles. The stem is composed of parenchymatous ground tissue and xylem and phloem confined to portions of small cambial segments. However, development of new cambial segments can be observed from the obliterating ray parenchyma, the outermost phloem parenchyma and the secondary cortical parenchyma. Initially cambium develops as small segments, which latter become joined to form a complete cylinder of vascular cambium. Each cambial ring is functionally divided into two distinct regions. The one segment of cambium produces thick-walled lignified xylem derivatives in centripetal direction and phloem elements centrifugally. The other segment produces only thin-walled parenchyma on both xylem and phloem side. In mature stems, some of the axial parenchyma embedded deep inside the xylem acquires meristematic activity and leads to the formation of thick-walled xylem derivatives centrifugally and phloem elements centripetally. The secondary xylem comprises vessel elements, tracheids, fibres and axial parenchyma. Rays are uni-multiseriate in the region of cambium that produces xylem and phloem derivatives, while in some of the regions of cambium large multiseriate, compound, aggregate and polycentric rays can be noticed.

Morfo-anatomia caulinear de nove espécies de Orchidaceae

Foram analisados sob o ponto de vista morfo-anatômico os sistemas caulinares (caule aéreo, rizoma e pseudobulbo) de nove espécies de Orchidaceae (Catasetum fimbriatum, Dichaea bryophila, Encyclia calamara, Epidendrum campestre, Epidendrum secundum, Miltonia flavescens, Pleurothallis smithiana, Stanhopea lietzei e Vanda tricolor). Comparando-se as espécies foi possível reconhecer uma certa uniformidade na organização interna dessas estruturas. Os rizomas e caules aéreos são revestidos por epiderme unisseriada, apresentam córtex parenquimático e feixes vasculares colaterais distribuídos em dois ou mais anéis no cilindro central. Os pseudobulbos possuem epiderme unisseriada recoberta por espessa cutícula e feixes vasculares colaterais distribuídos irregularmente no tecido parenquimático fundamental, que é formado por células grandes e pequenas com grande quantidade de espaços intercelulares.

Developmental morphology of the thalloid Hydrobryum japonicum (Podostemaceae)

We describe the unique development and branching of lobed thalli in Hydrobryum japonicum. Lobe formation begins with meristem initiation at random sites near the thallus margin fringed by protective tissues. As the protective tissues are successively peeled off particularly in the growing new lobes, the lobes become naked and then become fringed again by new protective tissues that develop from the marginal part of the new meristems. Subsequently the meristems become less active and are differentiated into parenchymatous ground tissue at maturity. The random pattern of meristem formation during the sporadic development gives rise to a nonorderly branching pattern of the thalli. Some other lobes (∼10%) are regenerated from injured parts of the thalli. The vegetative shoots arise endogenously near the thallus margin and are enclosed by the nonvascular strand nets. The rudimentary shoot apices remain embedded in the thalli. The thalli, though remarkably different from typical roots of other angiosperms, might be extremely transformed roots.

In vitro germination and seedling development of Dalzellia zeylanica (Gardner) Wight (Podostemaceae)

Seeds were germinated aseptically on thermocole cubes in 1/5 strength Murashige and Skoog's (1962) liquid medium (MS). The mature embryo has two well-developed cotyledons but lacks a plumule and a distinct radicle. The embryo emerges from the seed by the elongation of cotyledons and hypocotyl. The epidermal cells at the radicular pole elongate to form rhizoids. Proliferation of cells of the plumular pole gives rise to six to eight leaf primordia. An endogenously formed protuberance in the hypocotyledonary region develops into a green, dorsiventral thallus. The margins of the thallus also bear leaves. The presence of a band of small meristematic cells (five or six layers thick) below the apical mantle of large irregular cells has been seen in paradermal sections of thallus tips. Presumably they participate in the growth of the thallus. A vertical section of the thallus shows parenchymatous ground tissue and a strand of vascular tissue in the middle of the thallus which divides to supply the branches of the thallus. Tracheary elements have spiral/annular thickenings. Sieve elements showed callose when stained with aniline blue and viewed under a fluorescence microscope.