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The pits on parenchyma cell walls facilitate transfer of liquids between adjacent cells in the bamboo. To better understand the structure-function relationship of the pits, the structural characteristics of the pits in bamboo parenchyma cells need to be investigated. In this study, the pit structures were studied by field-emission environmental scanning electron microscopy (SEM). The samples included the native structure and the replica structure via resin castings. The results showed that the parenchyma cells possessed various shapes and the pits were diverse. Parenchyma cells exposed both simple and bordered pits. Pitting between vascular parenchyma cells (VPCs) was similar to that of the metaxylem vessel. In particular, a branched pit structure was found for the first time in the parenchyma cell.

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Not only are vessel pits vital for the passage of sap into adjacent cells, but their anatomical morphology is also used as a tool to identify bamboo species. However, detailed studies comparing the pits’ structural parameters in culms of species with three rhizome types: sympodial bamboo, amphipodial bamboo, and monopodial bamboo, are lacking. Scanning electron microscopy (SEM) observations were conducted to obtain the qualitative and quantitative characteristics of vessel pits in sympodial, amphipodial and monopodial bamboos, from twelve bamboo species in eight genera. Sympodial bamboos possess small and ovoid bordered pits, whereas amphipodial bamboos contain an abundance of slit-like pits, with the greatest pit membrane length occurring in the vessel wall. Both minute and large pit sizes can be found in monopodial bamboos. This study identified the first compound pits ever to be found in a bamboo species and these were found to occur more frequently in amphipodial and monopodial bamboos than in sympodial bamboos. Using the distribution frequency of the pit chamber’s horizontal diameter, we were able to determine pit size as being either small, medium or large. The striking differences in the vessel pits’ qualitative and quantitative characteristics could be the result of different climate and environmental factors.

Bamboo is an anisotropic, hierarchical, and hygroscopic material. Moisture transport in bamboo is one of the most fundamental properties affecting almost all other physical and mechanical properties of the material. This study investigated the water vapor sorption behaviors of bamboo at various structural levels: cell walls, cells (with pits) and bamboo blocks. The specimens with two sorption directions, longitudinal (L) and transverse (T), were measured by saturated salt solution method and dynamic vapor sorption. The parallel exponential kinetics model was used to analyze the sorption kinetics. The results showed that at the cell wall level, the sorption rate and equilibrium moisture content (EMC) of cell wall in the L specimens were larger than those in the T specimens. The differences were probably caused by the looser cell wall layers in the L specimens. At the cellular scale, pits in the cell wall resulted in an enhanced sorption rate and EMC of the T specimens compared with the L specimens where the pits in the parenchyma cells were only distributed in the lateral walls but not in end walls. At the macro scale, the sorption rate and moisture content of bamboo blocks were largely controlled by the vessel cells. As a hierarchically-structured plant, bamboo performs the biological function of moisture transport at all these scales. This work helps improve the understanding of water transport behavior in bamboo, which may lead to better bamboo drying and impregnation processes.