Morfoanatomia e ontogênese do fruto e semente de Vernonia platensis (Spreng.) Less. (Asteraceae)

Asteraceae possui cerca de 23.000 espécies e Vernonieae tem sua maior representatividade no Brasil, sendo Vernonia o maior gênero da tribo. Devido à ampla ocorrência nos Cerrados, V. platensis foi selecionada para a realização deste trabalho, que objetiva descrever a morfoanatomia e o desenvolvimento do pericarpo e da semente desta espécie, comparando os resultados com a literatura. O material coletado foi processado segundo técnicas usuais. O ovário é ínfero, bicarpelar, sincárpico, unilocular, com um óvulo anátropo, unitegumentado, tenuinucelado, formado em placentação basal. A parede ovariana é homogênea, com células mais densas perifericamente. O tegumento possui três regiões, destacando-se evidente endotélio. Na maturidade, a maioria das camadas colapsa, mantendo-se as fibras mesocárpicas externas; o pápus duplo persiste formado por células lignificadas. A semente madura apresenta testa restrita a uma faixa de células colapsadas; o endosperma é celular, persistindo residualmente na maturidade, e o embrião exibe eixo hipocótilo-radícula axial, espesso e curto. Em apenas 40% das cipselas maduras analisadas, há sementes completamente desenvolvidas. As observações deste trabalho corroboram pesquisas anteriores com Asteraceae, mas destaca-se o papel nutritivo do tegumento no desenvolvimento seminal e a baixa produção de sementes em V. platensis.The Asteraceae comprises approximately 23,000 species and Vernonieae is best represented in Brazil; Vernonia is the largest genus in this tribe. Due to occurrence in extensive areas of Cerrado, Vernonia platensis was selected for this work that aims to describe the morphology, anatomy and development of the pericarp and seed of this species, comparing the results with the literature. The collected material was processed by conventional techniques. The ovary is inferior, bicarpellate, syncarpous, unilocular with a single anatropous ovule, unitegmic, tenuinucelate, attached in a basal placenta. The ovary wall is homogenous with dense cells peripherally. The integument has three zones, with a conspicuous endothelium. At maturity, most layers collapse, only the outer mesocarp fibers remaining; the double pappus persists and has lignified cells. The mature seed has a testa composed of collapsed cells; the endosperm is cellular, residual at maturity, and the embryo has a thick, short, and axial embryo axis. Completely developed seeds were found in only 40% of the mature cypselae evaluated. Our observations corroborate previous research with Asteraceae; we call attention to the nutritive role of the seed coat in seed development, and the low production of seeds in V. platensis

Establishment Of Dalbergia Miscolobium Benth. Seedlings, A Tree Species Of The Brazilian Cerrados [estabelecimento De Plantulas De Dalbergia Miscolobium Benth., Uma Especie Arborea Dos Cerrados Brasileiros]

Cerrado is a typical Brazilian vegetal formation, considered neotropical savanna, that covers about 25% of its area, under a typical tropical climate, with rainy summer and dry winter. The water availability in the soil under cerrado vegetation is not constant neither uniform due to the great rain fluctuations and also because the vegetation is very scattered. This work shows the establishment of a cerrado tree species Dalbergia miscolobium Benth., from seeds, taking into account the rain fluctuations at which the seeds are submitted since fruit dispersion which occurs during the dry season. The fruits, dispersed in May, remained in the soil with viable seeds until the beginning of the constant rainfall, in September, when started the major seedling emergence. Seed viability, seedling emergence and survival were better when the fruits were protected from the direct radiation, kept buried and/or under shade and in a place without herbivores. Occasional rainfall during the dry season also allowed seedling emergence, but the survival was zero because the inadequate water availability for seedling growth.4013340Arasaki, F.R., Felippe, G.M., Germinação de Dalbergia violacea, uma espécie dos cerados (1987) Revista Brasileira de Biologia, 47, pp. 457-462Augspurger, C., Irregular rain cues and the germination and seedling survival of a Panamanian shrub (Hybanthus prunifolius) (1979) Oecologia, 44, pp. 53-59Barros, M.A.G., Caldas, L.S., Acompanhamento dos eventos fenológicos apresentados por cinco gēnerös nativos do cerrado (Brasilia-DF) (1980) Brasil Florestal, 10, pp. 7-14Blain, D., Kellman, M., The effect of water supply on tree seed germination and survival in a tropical seasonal forest in Veracruz, Mexico (1991) Journal of Tropical Ecology, 7, pp. 69-83Continho, L.M., O conceito de cerrado (1978) Revista Brasileira de Botânica, 1, pp. 17-23Evans, C.E., Etherington, J.R., The effect of soil water potential on seedling growth of some British plants (1991) New Phytologist, 118, pp. 571-579Ferri, M.G., Nota preliminar sobre a vegetaçāo do cerrado em Campo Mourão (Paraná) (1960) Boletim da Faculdade de Filosofia, Ciências e Letras da Universidade de Sāo Paulo, 17, pp. 109-115Ferri, M.G., Ecologia dos cerrados (1977) IV Simpósio Sobre o Cerrado - Bases para Utilizacāo Agropecuária, pp. 15-36. , M.G. Ferri (ed.) Editora Itatiaia e EDUSP, Belo Horizonte e Sāo PauloFranco, A.C., Souza, M.P., Nardoto, G.B., Efeito dos fatores ambientais no estabelecimento e crescimento de Dalbergia miscolobium (1993) Resumos do XLV Congresso Nacional de Botânica, p. 396. , Sociedade Botânica do Brasil (ed.) Sāo LeopoldoLabouriau, L.G., Válio, I.F.M., Salgado-Labouriau, M.L., Handro, W., Nota sobre a germinaçāo de sementes de plantas de cerrado em condições naturais (1963) Revista Brasileira de Biologia, 23, pp. 227-237Labouriau, L.G., Válio, I.F.M., Heringer, E.P., Sobre o sistema reprodutivo de plantas dos cerrados. I (1964) Anais da Academia Brasileira de Ciências, 36, pp. 449-464Mayer, A.M., How do seeds sense their environment? Some biochemical aspects of the sensing of water potential, light and temperature (1986) Israel Journal of Botany, 35, pp. 3-16Oliveira, P.E.A.M., (1991) The Pollination and Reproductive Biology of a Cerrado Woody Community in Brazil, , PhD Thesis, University of Saint Andrews, Saint AndrewsOliveira, P.E., Silva, J.C.S., Reproductive biology of two species of Kielmeyera (Guttiferae) in the cerrados of Central Brazil (1993) Journal of Tropical Ecology, 9, pp. 67-79Rawitscher, F., Ferri, M.G., Rachid, M., Profundidade dos solos e vegetaçāo em campos cerrados do Brasil meridional (1943) Anais da Academia Brasileira de Ciências, 15, pp. 267-294Reis, A.C.S., Climatologia dos cerrados (1971) III Simpósio Sobre o Cerrado, pp. 15-25. , M.G. Ferri (ed.) Editora Edgard Blücher e EDUSP. São PauloSarmiento, G., Goldstein, G., Meinzer, F., Adaptative strategies of woody species in neotropical savannas (1985) Biological Review, 60, pp. 315-355Sassaki, R.M., (1995) Dalbergia Miscolobium Benth., Aspectos da Biologia Reprodutiva e do Estabelecimento de Plântulas, , Tese de Doutorado, Universidade Estadual de Campinas. CampinasSassaki, R.M., Felippe, G.M., Viabilidade de sementes de Dalbergia miscolobium Bentham (Fabaceae) (1992) Revista Brasileira de Botânica, 15, pp. 1-3Schupp, E.W., Seed and early seedling predation in the forest understorey in treefall gaps (1988) Oikos, 51, pp. 71-78Snedecor, G.W., (1962) Statistical Methods, , Iowa University Press, IowaVälio, I.F.M., Moraes, V., Sobre o sistema reprodutivo de plantas de cerrado. II (1966) Anais da Academia Brasileira de Ciências, 38, pp. 220-22

On Surface Plasmons In Porous Silicon: Measurements Of The Electron Energy Loss In Etched Silicon Nanocrystals

Surface plasmons resulting from the interaction of the electron beam of a transmission electron microscope with porous silicon nanoparticles were measured. The inelastic scattering of fast electrons in H-covered silicon nanocylinders shows a peak at ∼5.5 eV. A gradual decrease of the first and second order plasma volumetric absorption simultaneous with a constant surface mode absorption amplitude was measured for decreasing silicon-slab thicknesses. Competitions between bulk and surface effects show, for the volume mode peak at 16.9 eV, a damping factor increase of ∼5 eV. The measured silicon particle diameter was ∼15 Å and a value of the dielectric constant is estimated from the surface plasmon data at 8.5, which is in agreement with recent theoretical work on the modified dielectric constant in quantum confined systems. © 1996 American Institute of Physics.20