PURSE 2001

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https://ir.lib.pdn.ac.lk/handle/20.500.14444/48

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Browsing PURSE 2001 by Subject "Anatomy"

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    Anatomy and categorization of pegmatites around Moragahakanda area
    (University of Peradeniya, Peradeniya, Sri Lanka, 2001-11-16) Pitawala, A.
    Pegmatitic occurrences are commonly observed in the proposed Moragahakanda- reservoir area. Most of them are characterized by economically important minerals such as quartz, feldspar and mica. At present, some pegmatites are mined for needs of the industry and there is a surplus of raw materials. As a result, there has not been any serious attempt to determine the extent and distribution of pegmatites. Three types of pegmatite occurrences, which are genetically different from each other, are observed. The older occurrences formed perhaps due to metamorphic events contain coarse to very coarse grains (up to few ern) of quartz and feldspar as major minerals and amphibole and mica as accessory minerals. They are smaller light coloured bodies several meters in length. On the other hand, dark coloured pegmatites are characterized by coarse to very coarse grains (up to several em) of pyroxene, amphibole and mica and they are occasionally associated with dykes of pyroxenite. They occur as bands parallel to the general trend of surrounding metamorphic rocks. The mineralogical composition and the filed relationship suggest that these bodies had formed at greater depths, perhaps subsequent to a metamorphic event. However, younger, strongly zoned pegmatites may have been formed at shallow depths. They are mainly made up of mega size crystals (up to several meters) of quartz and feldspar. The minor mineral constituent of the bodies is mica. Fluorite, tourmaline and opaque minerals occur as accessory minerals.
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    Investigation of Root Anatomy of Rice (Oryza Sativa) and Maize (Zea Mays) Grown in Aerated and Stagnant Conditions
    (Unviersity of Peradeniya, Peradeniya, Sri Lanka, 2001-11-16) Naganathan, M.; Gunawardena, A. H. L. A. N.
    Plants in the environment face different types of stresses such as salinity, drought, an water logging. Water logging is considered as a major stress in some areas. Plants have sever mechanisms to survive under flooded condition. Development of adventitious roots, superficial roots, increased branching of roots and the formation of Aerenchyma are considered to be the mechanisms to survive under flooded conditions. Aerenchyma facilitates gas diffusion between roots and the aerial environment. Some cells in the cortical region die to form aerenchyma. Bo the casparian bands and the suberin deposits in endo- and exodermis and suberized sclerenchyma layer act as main barriers to water flow and air movement in monocot roots. As a result radial oxygen loss is prevented. Rice and Maize plants were grown hydroponically in an incubator at 25C under aerated and stagnant conditions. Root lengths were measured daily and a mark was given at a distance of 10 mm from the root tip of the plants. Free hand cut sections of roots were taken using a razon blade and stained with Sudan 7B. These sections were viewed under light microscope an photographed. Some sections were stained with Berberine Aniline Blue and observed under Fluorescent microscope. Root growth was high under aerated condition in maize compared to the stagnant condition over time. However, in rice, root growth was more or less similar in aerated and stagnant conditions. Increased pH was observed under aerated condition, while a declined pH in stagnant condition over time. The different layers of a monocot root (epidermis, exodermis, scierenchyma layer, cortical parenchyma, endodermis, pericycie and stele core) were observed clearly. Formation of aerenchyma was observed in maize roots grown in stagnant conditions, but not in aerated condition. In rice roots aerenchyma was observed in both aerated and stagnant conditions. Initiation of aerenchyma was observed in the mid cortex region in rice and maize root (stagnant condition). Both the casparian bands and suberization in endodermis and exodermis, were prominent in rice and maize roots grown under stagnant condition than in aerated condition. In addition, a very thick scierenchyma layer also was present in rice roots grown under stagnant condition. The results of this anatomical study will be useful in plant breeding programs especially in the production of varieties with constitutive aerenchyma and in the production of drought tolerant varieties.