Anatomical agreement on specific characteristics of Begonia
- (0) Download
https://www.eduzhai.net International Journal of Plant Research 2013, 3(3): 27-38 DOI: 10.5923/j.plant.20130303.03 Anatomical Protocol of Begonia dipetala Graham for the Specific Identity of the Plant Isaivani Indrakumar1,*, S. Karpagam1, P. Jayaraman2 1Department of Botany Queen M ary’s College, Chennai, 600004, India 2Plant Anatomy Research Centre, West Tambaram, Chennai, 600045, India Abstract The botanical identity of Begonia dipetala Graham remained controversial, since its time of discovery in 1826. It was considered to be synonymous with B.malabarica Lamarck which is endemic to Malabar of Kerala India. Irmcher (1960) declared that D.dipetala Graham is an independent taxon. Santhosh et al.(2005) provided morphological features of B.dipetala and confirmed its identity. The present study deals with the anato mical parameters of leaf, petiole, internode, rhizo me and root of B.dipetala. The morphological features of flowers and leaves are described briefly. The results of the study are believed to supplement the external features and to circumscribe the taxonomic status of B.dipetala. The present investigation aims at co mparison with those of other members of Begoniaceae published by Solereder (1908) and Metcalfe and chalk (1957). Significant differences were observed between B.dipetala and other species of Begonia. It is suggested that B.dipetala can be treated as an independent species. Keywords Begonia dipetala Graham, B. Malabarica Lamarck, Identitiy, Anatomical Parameters 1. Introduction Begonia of Begoniaceae includes 900 species at global level. In India there are 45 species. In Ta mil Nadu eight species have been recorded. In terms of number of species, Begonia may be an insignificant taxon; when its economic values are considered, it is of high hort icultural importance. The species of Begonia bear foliage-leaves and flowers which are ethereal in architecture and will captivate any casual observer. Furthermore, certain species of Begonia, especially B. malabarica, are cred ited with med icinal properties. The ethnic communities of Western Ghats of South India, attribute many pharmaceutical efficacies to Begonia. B.dipetala Graham is an archaic species and its history of discovery dates back to early part of nineteenth century. It was first discovered in the Western Ghats of Bo mbay, India in 1826 by Johnstone and was described by Graham in 1828. In 1859,Th waites  described a new variety , D. malabarica var dipetala, Clarke (1879) continued to use B.di petala as a variet y o f B.mala bari ca. Based on the examinat ion o f herbariu m specimens o f B.dip etala , de Cand o lle des cribed it as B.mal aba rica , wh ich was considered to b e an inco rrect ident ificat ion. Irmch er proved that B.di petala Graham is clearly d istin ct fro m B.malabarica Lamarck and therefore, cannot be a variety of * Corresponding author: email@example.com (Isaivani Indrakumar) Published online at https://www.eduzhai.net Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved it. This tenet was further strengthened by the findings of Santhosh et al. who provided the taxono mic circu mscription of B.malabarica collected fro m Kerala, India. The present study focuses on the microscopic features of different organs of B.dipetala to expand the diagnostic dimensions of the taxon and to supplement the external characters with the internal features to confirm the identity. 2. Literature Review Anatomical studies on Begonia in general, and B.dipetala in particu lar are very much lacking, barring a few frag mentary studies. Rose and Hurd-Kareer recognised two physiological ly different types of cells, sharply differentiated when the leaf sections were put in the indicator solutions for about 15 minutes. They observed that most of the cells lose their high acidity and the colour of the cells changed towards the alkaline fo rm of the die. Other cells called “Specialised Cells” retained their acidity and the acid colour of the cells remained indefinitely. These specialised cells contain calciu m o xalate crystals of druses. The authors confirmed the physiological differences between the two types of leaf, by immersing the sections in solution by the oxidase reagents benzidine and gum guaiacu m; the crystal containing cells stain blue while, other cells do not stain. Watson and Dall witz have given a brief account of anatomy of leaf and stem apart fro m external features of the species of Begoniaceae. The authors reported “pearl – 28 Isaivani Indrakumar et al.: Anatomical Protocol of Begonia dipetala Graham for the Specific Identity of the Plant glands”, hydathodes and stomata confined to the lower surface and the stomatal types varied fro m anisocytic, paracytic, diacytic to cyclocytic with 3 – 6 subsidiary cells arranged in two rings. They have also mentioned that presence of one or mo re hypodermal layers on the adaxial side of the lamina. Cystoliths and sclerenchymatous idioblasts are present or absent; minor veins do not have phloem elements. The stem has superficial cork-camb iu m; the nodes are trilacunar and pentalacunar, cortical bundles and medullary bundles are present or absent. A brief account on the structure of the mid rib of Begonia elatior x hybriden was given by Anisoara Stratu et al.. These authors observed that the lamina between the veins is thin. The mesophyll of the lamina has bifacial heterofacial structure. The adaxidal epidermal cells are tangentially elongated and thick. The midrib wall is raised on the adaxial side. In 1830, Hooker described the characteristics epidermal hairs, glands and structure of stem of Begonia longipes. Hil debrand and Fellerer published an outstandi ng work on the systematic anatomy of Begonia. These authors considered mainly the cystoliths and cystosphere formation as systematic characteristics for the analysis of Begonia. They contemplated that these characters were proof for relationships with Cucurbitaceae. Haberl andt described the sclerenchyma distribution in the leaves of B.nelumbifolia, B.pustulata and B.violifolia. Hailler proposed phylogenetic relat ionships of the anchor-hairs of Begonia species with the hairs in the composital member namely Hypochoeris aeltinensis. Pneumatothodes have been described by Vouk in stem of B.vitifolia, wh ich resemble and replace typical lenticels. Fotsch provided detailed account of anatomical aspect of Begonia. Fellerer and Boghdan studied and described mu lticellu lar nonglandular and captitate and noncapitates trichomes of Begonia. Multiple epidermis has been reported in Begonia by several workers (Boghdan and Barkely,; Barkley and Hozid,; Boghdan,. The tribals, Paliyans and Pulayans of Palani Hills of Tamil Nadu seem to use the paste of the stem of B.malabarica to cure the pimp les and for cooling effects (Ganesan et al.,). Santhosh et al. traced the history of the discovery of Begonia in India, starting fro m the period of Rheede. The authors elucidated the identity of Rheede’s Tsjerianarinampuli as Begonia malabarica Lamk. Clarke while studying Begoniaceae of Brit ish India, included B.malabarica with two more variet ies viz; var.dipetala and var.hydrophila. Gamble followed Cl arke and described the species occurring in Madras Presidency as B.malabarica. After elaborate discussion of various reports on Begonia by different investigators, the authors proposed a dichotomous key to distinguish B.dipetala, D.dipetala var. hydrophila, B.malabarica and B.fallax. In B.dipetala the male and female flowers consistently have 2 perianth lobes; the fruits are attenuated at the apex; the wings are rounded obtuse at the base and wings are rounded along the margins. B.dipetala var hydrophila is characterized by obovate – rounded fruit which is obtuse at the base and the wings are obtuse or sub angulate. Begonia malabarica differs fro m Begonia dipetala in having 4 perianth lobes in male flo wers and 3 perianth lobes in the female flo wer; the perianth lobes and the capsule are pilose on the outer sides (Santhosh et al.,). Rajbhandary et al. traced the origin and dispersal of Asian. According to the concept of the authors the genus Begonia began to diverge in Africa during the Oligocene and the current hotspot of diversity for the genus in China and South East Asia must therefore be the result of an eastward dispersal of or migrat ion across the Asian continent. The authors considered the role of Himalayas as a mesic corridor facilitating this migration and constructed a time calibrated mo lecular phylogeny using ITS sequence data. According to the investigators the Himalayan species of Begonia fall under two groups: 1, an unresolved grade of tuberous, deciduous species of unknown geographic origin, with evidence of endemic rad iations in the Himalayan region beginning c.7.4 Ma coinciding with the outset of the Asian monsoon. 2, a group of evergreen rh izo matous species with a probable origin in China, which has migrated to the Himalayan region c.5.1 Ma coincid ing with an intensification of the monsoon. Anisoara et al. studied certain decorative flowering plants with respect to the physiological and anatomical aspects. The study includes Begonia elatior X hybriden. Their results showed that water content in flower buds and flowers is highest, low values in the leaf; cell ju ice concentration was low; chlorophyll -a :chlorophyll -b content was in low rati o. The thickness of the lamina is less, the mesophyll is bifac ia l – heliofac ial. The ada xia l epidermis has larger and slightly elongated cells, and abaxial epidermal cells are thin. The midrib is obviously prominent. Based on the observation, the authors believe that in Begonia elatior X hybriden, the internal factors influence the exchange of gas between the leaf and environ ment and exchange of substances within the tissues. The values of various parameters are specific physiological indicators of the plant. McLellan considered that many co mbinations of features did not occur at random either due to functional constraint or genetic correlation. The distribution of variation in leaf morphology in the highly variable Begonia dregei species complex was examined in natural population and in F2 offspring fro m a cross between plants fro m t wo populations. The author quantified leaf shape using several morpho metric measures; trichomes on the leaves were counted and measured. Correlat ions between leaf shape and the numbers and size of the tricho mes were examined. There were significant correlations between the shapes of the leaves and the presence of number and size o f the trichomes among populations and in the hybrid plants. According to the author deeply incised leaves had longer and larger number of trichomes at the sinuses. Higher number of t richo mes on the leaf surfaces occurred together with the tricho mes at the petiole and on the abaxial surface. The potential for International Journal of Plant Research 2013, 3(3): 27-38 29 independent evolution of the leaf shape and trichomes in this group was reported to be limited. Santhosh considered B.dipetala var. hydrophila is an independent taxon and it is not a variety of B.malabarica as per the description of Clarke. The former species is endemic to the Western Ghats of India. It seems that B.dipetala var hydrophila is often confused with B.fallax de Candole which stimulates very much former species. However, the latter species has lax inflorescence, mo re robust habit, male flo wers with 4 perianth and female with 3 perianth lobes. Ku et al. reported a new species from China which has been named as B.pengii S.M.Ku & Yan Lieu. The authors have provided somatic chro mosome number and karyotype, detailed morphological descriptions with clear illustrations, leaf anatomy including tricho me mo rphology and ecology of the species. Begonia tenera Dryander is a species endemic to Sri Lanka. This species has been reported from India by Shaju et al. B. tenera is a perennia l acaulescent herb with ovate or rotundate leaves; inflorescence is racemose, umbellate; tepals 2+2, wh ite with pinkish periphery; tepals of the female flower are 5 in t wo whorls. Santhosh and Roy have provided taxonomic circu mscription for Begonia aliciae C.E.C. Fischer, a niche specific endemic species of the Western Ghats of Kerala and Tamil Nadu. Santhosh et al. rediscovered this species after a lapse of 64 years fro m the type locality fro m where it was first collected by Edward Barnes and the specific epithet was provided by Fischer B.aliaceae is scapigerous herb. The male flowers have four perianth lobes and female flowers have six perianth lobes. The ovary is 2 celled and two winged. Makarand et al. reduced B. aliciae to B. crenata Dryand. Yoo Sung lee made elaborate studies of stemanatomy of about 44 species of Begonia collected fro m different localities. The author studied the first internodes or the fifth inter nodes and the tissues of the inter nodes; collenchymas, sclerenchyma, secondary vascular tissues, periderm and trichomes; the conditions of the vascular ring and vascular bundles were analy zed during the study. The observation of different species was compared. 3. Aim and Scope of the Present Study Care ful perusal of literature so fa r revie wed may indicate that the systematic circu mscription of Begonia dipetala has remained enig matic for a long time. After a series of morphological studies, some consensus have been reached for the identity of the specific name of Begonia dipetala Santhosh kumar,. We believe that the microscopic features of Begonia dipetala may supplement the morphological parameters, especially when the specimen lacks the floral parts. It has been shown that certain qualitative microscopic data are less prone to changes due to environmental stress. We aimed such of those features that are constant and consistent for Begonia dipetala and to prepare a protocol of data for applying such data for botanical identification of species. 4. Materials and Methods Materials for the present study were collected fro m Hills near Salem (Tamil Nadu; India) during different seasons. The species identity was confirmed by Dr. Santhosh Kumar, Jawaharlal Nehru Tropical Botanical Garden and Research Institute, Palode, Kerala and the identification was confirmed by Botanical Su rvey of India, Ho wrah . (CNH13/ 2013/Tech II/958). Herbaria of voucher specimens were prepared and the specimens are lodged in the Plant Anatomy Research Centre, West Ta mbara m, Chennai - 45. Different parts of the plant, such as leaf (midrib and lamina), petio le, stem, rhizo me and roots were fixed in FAA (Formalin: Acetic acid : 70% Ethanol; 5:5:90) fo r 24 hrs. After fixat ion the specimens were washed, dehydrated by passing through Tertiary butyl alcohol (TBA) series following the procedure of Sass, 1940. After dehydration, the specimens were infiltrated with paraffin wax (melting point 56-58°C) ad embedded in the paraffin blocks. Sections were cut using Rotary microto me at a thickness of 10µm. Sections were stained with Toluidine blue (0.01%) aqueous solution. Photomicrographs were prepared with Nikon trinologular mic roscope and Nikon digita l ca mera . 5. Observation 5.1. External Features Begonia dipetala is a herb or sub - shrub growing predominantly in moist or water saturated habitats (Fig.1). It has thick stem which is pin k or light red. The leaves are alternate (Fig. 2), distichous,obliquely ovate, semi cordate at base, apex acu minate (Fig.3&4). The inflorescence is an axillary raceme (Fig.2&5). The plant is monoecious with male and female flowers located on the same in florescence; the male flowers are on the upper part of the peduncle, the female flowers being on the lower part (Fig.5&6). The flowers are white or pale p ink. The flo wers have two petals. The ovary is pink or red with truncate apex and three memb ranous wide semicircular wings (Fig 11). The stigmatic colu mn bears spherical bodies (Fig.9&10). Ovary is tricarpellary, triangular in sectional view. Ovules are on axial placentation (Fig.12). The stamens are nu merous forming a dense cluster located in between two petals (Fig.7&8). The seeds are elliptical, dark co loured, with reticulate, pro minent thickenings on the surface (Fig.13). 30 Isaivani Indrakumar et al.: Anatomical Protocol of Begonia dipetala Graham for the Specific Identity of the Plant Fi gure 1. Begonia dipetala in it s nat ural habitat – Moist crevices of rocks F – Female, M – Male Figure 5. An inflorescence showing upper female flower and lower male flower In – Inflorescenc, Fr – Fruit, OFr- Old Fruit Figure 2. Flowering shoot system showing a phyllotaxy and inflorescence F – Female, M – Male Figure 6. Female and male flowers – Enlarged AdS – Adaxial Surface Figure 3. Leaf showing adaxial view and shape And – Androecium Figure 7. T wo petals of the male flower open showing the cluster of st amen s AbS – Abaxial Surface Figure 4. Leaf in abaxial view Ant – Anther Figure 8. Staminal cluster spread apart International Journal of Plant Research 2013, 3(3): 27-38 31 Figure 9. Female flower with two petals and stigmatic lobes Fi gure 10. St igmat ic lobes – Enlarged Se – Seeds Figure 13. Surface features of the seeds 5.2. Anatomical Features 5.2.1. Leaf The leaf is undulate in transectional view with ridges and furrows due to the prominent veins and thin lamina (Fig.14). The veins are mu ltistranded. The number of vascular strands varies depending upon the size of the veins. The midrib has two larger abaxial vascular bundles and two s maller adaxial bundles (Fig.14). The bundles are collateral and the xy lem units of the adaxial, abaxial bundles are ju xtaposed (Fig.14). The smaller lateral veins have two vascular bundles which are adaxial and abaxial in position (Fig.14). The epidermal cells of the veins are thick with thin walls and less prominent cuticle. The ground tissue of the veins consists of polygonal thin walled, co mpact parenchyma cells. W – Wing Figure 11. A mature winged fruit AbS – Abaxial Strand, AdP – AdaxialPart, AdS – Adaxial Strand, LV – Lateral Vein, MV – Mid Vein Figure 14. Cross section of the leaf through mid vein and lateral vein W – Wing, OVL – Ovules, OV–Ovary Figure 12. Cross section of the ovary showing the placentation and wings The lamina is 130-150µm thick. It is dorsiventral and heterofacial. The adaxial ep idermis is uniseriate and the cells are 30-40µm thick. The abaxial ep idermis is also uniseriate and thinner than the adaxial epidermis. The cells are narrow and cylindrical. It is stomatiferous. The stomata are raised above the level o f ep idermis and they have pro minent stomatal ledges (Fig.15). The mesophyll includes adaxial band of palisade cells which are 30µm in height. The spongy parenchyma is four layered and the cells are small, spherical or lobed. The marginal part of the leaf is straight and semi circular; the epidermal cells of the margin are slightly larger 32 Isaivani Indrakumar et al.: Anatomical Protocol of Begonia dipetala Graham for the Specific Identity of the Plant and thick walled (Fig.16). The mesophyll tissue remains stoma (Fig.18). unchanged (Fig.16). AdE – Adaxial Epidermis, PM – Palisade Mesophyll SM – Spongy Mesophyll Figure 15. T.S. of lamina – Enlarged AW – Anticlinal Wall Figure 17. Surface view of the adaxial epidermal cells LM – Leaf Margin, AdE – Adaxial Epidermis, MT – MesophyllT issue, AbE – Abaxial Epidermis Figure 16. Marginal part of the lamina 5.2.2. Ep iderma l Trichomes The epidermal t richo mes are abundant on all parts of the leaf. Two types of tricho mes are seen. Non-glandular trichomes are more frequent on the adaxial side. They are mu lticellu lar, and unbranched. The cells are vertically oriented and thin walled (Fig.19). The tricho mes are emergences or shaggy type (Fig.19,30&31). The glandular trichomes are the second type which is more co mmon on the abaxial side of the lamina. The glands are peltate type. It consists of a two celled short stalk and circular plate of 4 celled head, wh ich is at right angles to the stalk. The head part of the gland is darkly stained and secretory in function (Fig.29). The gland is 60µm high and 70µm wide. SC – Subsidiary Cells, GC – Guard Cells Fi gure 18. Abaxial epidermis showing st omatal type 5.2.4. Venation Pattern The lateral veins are thin and less prominent. They form fairly distinct rectangular and isodiametric vein-islets with long slender branched or unbranched vein-terminations (Fig.19). 5.2.3. Ep iderma l Tissue The adaxial ep idermis, as seen in surface view, consists of polyhedral, angular, thin walled cells with straight walls. The epidermis is apostomatic (Fig.17). The abaxial epidermis is densely stomatiferous. The stomata are either cyclocytic with four subsidiary cells encircling the guard cells or anisocytic with three unequal subsidiary cells around a VI – Vein – Islet, VT – Vein T ermination), Ve – Vein, Tr – Trichome Figure 19. surface view of the lamina showing venation pattern and distribution of trichomes 5.2.5. Petiole The petiole is 1.4mm thick and elliptical in outline; the International Journal of Plant Research 2013, 3(3): 27-38 33 surface is uneven. The epidermal cells are conical and thin walled. There are two or three layers of chlorenchyma cells and the remain ing ground t issue is thin walled parenchymat ous. The vascular system is mu ltistranded; there is a ring of 10 collateral vascular strands of different size and shape (Fig.20&21). cells in the inner part. The vascular t issue exhib its init ial stage of secondary growth. The primary vascular bundles are laterally interconnected by thin zone of secondary tissues in which the xy lem elements have not yet mature. Phloem occurs on the outer part of the xylem which has sclerenchyma cap (Fig.24&25). GT – Ground T issue, VB – Vascular Bundle Figure 20. T.S. of Petiole – Entire view Ep – Epidermis, Co – Cortex, VB – Vascular Bundle, Pi – Pith Figure 22. T.S. of Young stem Ep – Epidermis, Chl – chlorenchyma, Pa – Parenchyma, Ph – Phloem, X- Xylem Figure 21. T.S. of Petiole a sector showing vascular bundle 5.2.6. Stem The young stem is circu lar in cross sectional view with irregular ridges and furrows. The epidermis has thin walled intact cells. The cortex consists of outer three or four layers of thick walled co mpact cells and inner thin walled parenchyma cells. The vascular system is eustele type with several discrete bundles and parenchymatous medullary rays. The vascular bundles are radially stretched and collateral. Xylem elements are wide, angular and thin walled; they occur in two or three rows of rad ial mu ltip les (Fig.22&23). Sclerenchy ma caps are seen on the outer end of the phloem units of each bundle. Starch grains are common in the cortex and pith cells. Fairly thick stem has shallow ridges and furrows. Th in less prominent periderm with darkly stained two or three layers of cells occur on the surface of the stem. The cortex includes outer part of tangentially stretched cells and wide angular Pa – Parenchyma, Ph – Phloem, X- Xylem Figure 23. A vascular bundle of the young stem Pe – periderm, Co – Cortex, St – Secondary thickening, PC – Pith Canal Figure 24. T.S. of Old stem 34 Isaivani Indrakumar et al.: Anatomical Protocol of Begonia dipetala Graham for the Specific Identity of the Plant cells. The root has large polygonal parenchyma cells most of them containing darkly stained tannin contents (Fig.26&27). The vascular cylinder is solid, dense and is wavy in outline. The secondary phloem is wide and continuous comprising clusters of sieve elements. The secondary xylem includes central part o f darkly stained thick walled narrow fibers and a few diffusely distributed vessels. The outer part has fibres with wide lu men and narrow angular, mostly solitary vessels (Fig.27). The vessels are up to 40µm in diameter. Pe – periderm, Co – Cortex, BCF – Bundle Cap Fibre, Ph – Phloem, SX – Secondary Xylem, X- Xylem Figure 25. Primary vascular bundle and interfasicular seondary xylem element 5.2.7. Rh izo me The rhizo me is vertical thick cylinder of wh ich gives rise to roots on all sides. It is deeply ridged with wide furro ws. It consists of two or three layers of suberized periderm cells followed by rectangular or polygonal parenchymatous cortex (Fig.28). The vascular cylinder is thin and continuous, comprising inner part of conical primary xy lem units and outer compact mass of phloem. Secondary xylem consists of thin walled radial rows of cells (Fig.28). Secondary phloem occurs in prominent circular masses on the outer part of the xy lem cylinder. 5.2.8. Root Pe – periderm, Co – Cortex, Ve – Vein, SX – Secondary Xylem, SPh – Secondary Phloem Figure 27. T.S. of Root – A sector enlarged Pe – periderm Figure 26. T.S. of Root – Entire view A thick root measuring 1.8mm in diameter exhib its a thick periderm which is about five layered; the cells of the periderm are darkly stained and compact and cylindrical. The cortex has outer zone comprising radially oblong dilated Pe – periderm, Co – Cortex, SXC – Secondary Xylem Cylinder, PPh – Primary Phloem, PX – Primary Xylem, Pi – Pith Figure 28. T.S. of Rhizome – A sector 6. Discussion Begonia dipetala is established as an independent taxon. International Journal of Plant Research 2013, 3(3): 27-38 35 The identity of the specimen is based on morphological criteria Santhosh,. In the present study, microscopic features of vegetative organs of the plant are provided which are believed to throw mo re light on the diagnosis of the Begonia dipetala. In elaborate anatomical studies of the stems of Begonia, Lee tried to correlate the stem anatomy and sectional classification of Begonia. Lee remarked that according to many investigators of Begonia, the epidermis of the lamina is multilayered. He d isagreed with the observation of the previous authors and said in 44 species of Begonia which he studied have only unistratose epidermal layer. In the present study on Begonia dipetala also we could see only single layered epidermis both on the adaxial and abaxial sides of the lamina. According to Metcalfe and Chalk the lamina in the members of Begoniaceae has hypodermal layer of parenchyma cells; they also reported that stone cells, idioblasts and similar mechanica l ele ments are frequent in the mesophyll or around the veins; the palisade cells are locally replaced by stone cells; the vascular bundles are sometimes surrounded by collenchymas or elongated parenchyma cells. In the present observation of Begonia dipetala, the structure of the lamina is simp le and structure mentioned by Metcalfe and Chalk is not evident. The adaxial epidermis consists of highly dilated cells measuring 40µm thick. Beneath epidermis is a co mpact layer of short wide palisade cells which are 20-40 µm in height. The stone cells and the idioblasts are absent; the vascular system of the midrib is mu ltistranded comprising two pairs of vascular bundles in midrib and single pair in the lateral veins; the vascular bundles are adaxial and aba xial in position and they are ju xtaposed with the xylem poles (Fig.14). Th is aspect of the vascular system of the veins of the leaf has been given due accent by early investigators. It is felt that vascular structure of the veins may serve as a valuable source of botanical diagnosis of the plant. The epiderma l trichomes are said to be highly diversified and they have elaborately discussed by Solereder based on the studies of Fellerer  on the hairy covering in Begoniaceae. S olereder remarks that the epidermal hairy covering is exceptionally varied and is suitable for employ ment in specific diagnosis. Of different types of tricho mes described by Solereder, we could recognize in Begonia dipetala the shaggy trichomes, capitate and peltate glandular tricho mes. The shaggy trichomes are mu ltiseriate with thick basal part which gradually become conical at the tip or uniseriate, one or t wo celled t ip (Fig.30&31). A spherical darkly stained epidermal body is often seen at the terminal cell, which becomes shrunken deciduous at later stage. The shaggy trichomes do not form free mamillifo rm tips on the lateral sides as described by Solereder (Fig.30&31). Apart fro m afo re said trichomes, there are sessile, spherical dark b rown unicellu lar shinning bodies, seen within the angles of the marginal serrations and elsewhere on the lamina (Fig.32). This type of glands have not been recorded by the previous investigators. The brown shining glandular bodies have a short, broad, bowl shaped stalk cell and spherical body with thick walls and dark contents. Solereder remarks that the epidermal cells of the leaf are larger and have thick straight lateral (anticlinal) walls in Begoniaceae. The size of the epidermal cells is said to be emp loyed for the recognition of the sections of the genera or in the d iagnosis of indiv idual species within the same species. In Begonia dipetala, the epidermal cells, part icularly the adaxial cells are quite thick; the anticlinal walls are always thick and straight. The stomata are either cyclocytic with encircling subsidiary cells, or anisocytic with three unequal subsidiaries. These features of the epidermal tissues are of taxono mic values. Petiole with discrete bundles forming a ring and presence of medullary bundles with or without sclerenchyma e le ments have been said to be of diagnostic values for Begonia. In Begonia dipetala, there is neither medullary bundle nor sclerenchyma elements. The petiole is wavy in sectional view; there is a thin layer of chlorenchymatous cells inner to the epidermis. Isolated small co llateral bundles are organized in a ring (Fig.20&21). These features are specific for Begonia dipetala. The internode of Begonia has been studied by some investigators (Lee, 1974). According to the available literature, the general features of interest are the cortical bundles and medullary bundles. In some of the species of both cortical and medullary bundles have been reported, in others either cortical bundles alone or only medullary bundles occur Lee,; Solereders,. Begonia dipetala lacks both cortical bundles and medullary bundles. The young stem has eustelic type of vascular system comprising several discrete primary collateral vascular bundles arranged in a ring. As the stem grows in thickness, medullary rays give rise to interfasicular camb ial strips which produce init ial secondary xy lem and phloem. The epidermal layer is unistratose. In the old stem, the epidermal layer and a subepidermal layer get comp ressed into thick dark surface on the stem. The superficial co rtical cells form a thin, less prominent periderm layers (Fig.22&24). Wide circular pith canal develops in the old stem due to lysigenous process of the pith cells. Begonia dipetala is a rhizomatous species having horizontal, succulent rhizo me. The rhizome consists of a wide hollo w central ho mogeneous parenchymatous cortex and a continuous vascular cylinder. The cylinder comprises several radially stretched collateral vascular bundles which are interlinked by interfasicular secondary xy lem-ph loem elements (Fig.28). The vessel elements are poorly differentiated both in the fasicular and interfasicular portions. The root has thick darkly stained outer zone of crushed epidermis; subsequently an incipient periderm is formed fro m the outer cortical cells. The secondary xylem cylinder is dense and solid comp rising sparsely distributed, thin walled, narrow angular vessels (Fig.26&27). The rhizo me and root do not possess any specific or unique features and they do not throw much light on taxonomic identity of B.dipetala. 36 Isaivani Indrakumar et al.: Anatomical Protocol of Begonia dipetala Graham for the Specific Identity of the Plant GB – Glandular Body, St – Stalk, AdE – Adaxial Epidermis Figure 29. A peltate glandular trichome on the adaxial side of the lamina Figure 32. Deeply coloured sub-sessile spherical glandular trichome on the lamina Dr – Druses Figure 33. Calcium oxalate druses in the mesophyll tissue of the lamina Figure 30. Nonglandular shaggy type of trichome Figure 31. Nonglandular shaggy type of trichome Dr – Druses Figure 34. Calcium oxalate druses in the mesophyll tissue of the lamina Ergastic substances of diversified chemical co mposition and morphological categories are persuasive in the tissues of all part of the plant. Calciu m o xalate crystals are most widespread storage material in plant. Unfortunately, there is much that remains obscure and opinions differ concerning the role that calciu m o xalate crystals play in the plant metabolism. Neutralisation of unwanted oxalic acid, reintroduction into metabolic cycle during the demand of calciu m ions, mechanical protection of the plants against
... pages left unread,continue reading
Free reading is over, click to pay to read the rest ... pages
0 dollars，0 people have bought.
Reading is over. You can download the document and read it offline
0people have downloaded it