Madeiras utilizadas na fabricação de arcos para instrumentos de corda: aspectos anatômicos

A madeira de pau-brasil (Caesalpinia echinata Lam.) é mundialmente empregada na confecção de arcos para instrumentos de corda, uma vez que apresenta características únicas de ressonância, densidade, durabilidade, beleza, entre outras qualidades, que a tornam ideal para tal uso. Diferentes amostras de pau-brasil, contudo, fornecem arcos com qualidades distintas. No comércio nacional outras madeiras estão sendo empregadas na produção de arcos. Realizou-se, neste estudo, uma análise qualitativa e quantitativa de diferentes amostras de pau-brasil com o objetivo de apontar diferenças na estrutura da madeira que possam contribuir para o entendimento das causas da variação na qualidade do arco, além da análise de outras espécies objetivando determinar, do ponto de vista estrutural, semelhanças ou diferenças com o pau-brasil. Conclui-se que variações no diâmetro dos vasos, distribuição e quantidade de parênquima axial e orientação dos elementos axiais e radiais são parâmetros que devem ser considerados quando se busca determinar as causas das diferenças na qualidade dos arcos de pau-brasil. Constatou-se que arcos de boa qualidade apresentam grã linheira e textura fina. Esta última característica decorre da menor proporção de vasos cujo diâmetro é reduzido, raios homogêneos e fibras com paredes espessas e/ou muito espessas. Assim, a relação entre a estrutura e a qualidade do arco está diretamente relacionada com as dimensões, a distribuição e a proporção das células do lenho

Differences in anatomy and potential hydraulic conductivity between root and stem of Caesalpinia echinata Lam. (Fabaceae)

We investigated the root and stem wood of Caesalpinia echinata Lam. to test the hypothesis that there are anatomical and water conductivity differences between both organs. Three trees about 20 years old were sampled in the Reserva Biológica de Mogi Guaçu, São Paulo State, Brazil. We observed quantitative anatomical differences between the root, heartwood, and sapwood of C. echinata that result in differences in water conductivity. The sapwood has higher potential hydraulic conductivity than the heartwood (when functional), and root. The higher proportion of axial parenchyma in the root could contribute to the storage of starch and water in unfavorable periods, which is important to the osmotic regulation of the daily water deficits, avoiding cavitation. The stem of C. echinata probably has a higher mechanical strength than the root due to its fibers with thicker wall

Differences in anatomy and potential hydraulic conductivity between root and stem of Caesalpinia echinata Lam. (Fabaceae)

We investigated the root and stem wood of Caesalpinia echinata Lam. to test the hypothesis that there are anatomical and water conductivity differences between both organs. Three trees about 20 years old were sampled in the Reserva Biológica de Mogi Guaçu, São Paulo State, Brazil. We observed quantitative anatomical differences between the root, heartwood, and sapwood of C. echinata that result in differences in water conductivity. The sapwood has higher potential hydraulic conductivity than the heartwood (when functional), and root. The higher proportion of axial parenchyma in the root could contribute to the storage of starch and water in unfavorable periods, which is important to the osmotic regulation of the daily water deficits, avoiding cavitation. The stem of C. echinata probably has a higher mechanical strength than the root due to its fibers with thicker wall

Structural responses of Ipomoea nil (L.) Roth 'Scarlet O'Hara' (Convolvulaceae) exposed to ozone

Troposphere ozone (O3) is an important photochemical pollutant due to its high reactivity and phytotoxicity. Plants can show microscopic damage caused by this gas before the detection of visible symptoms. The present study aimed to improve our knowledge concerning the effects of O3 on Ipomoea nil L. cv. Scarlet O'Hara leaves. Plants were exposed at a pollutant site in São Paulo city, with high levels of O3, and fumigation with O3 was also carried out. In plants exposed to the environment, without visible symptoms, hypersensitive response-like (HR-like) and protrusions in the cell walls was observed, indicating oxidative processes; in leaves with visible symptoms, there is epidermis breakdown and the palisade and spongy parenchyma collapse. Fumigation confirmed that microscopic damage occurring in the plants exposed to the environment was linked to the symptoms caused by O3. These results demonstrate that Ipomoea nil responds to stress induced by O3 with specific structural changes that precede visible symptoms