Soil plant atmosphere continuum Soil plant atmosphere continuum The soil-plant-atmosphere continuum (SPAC) is the pathway for water moving from soil through plants to the atmosphere. Continuum in the description highlights the continuous nature of water connection through the pathway. The low water potential of the atmosphere, and relatively higher (i.e. less negative) water potential inside leaves, leads to a diffusion gradient across the stomatal pores of leaves, drawing water out of the leaves as vapour. As water vapour transpires out of the leaf, further water molecules evaporate off the surface of mesophyll cells to replace the lost molecules since water in the air inside
Smear layer 1975 McComb and Smith first described the smear layer. They observed an amorphous layer of debris, with an irregular and granular surface, on instrumented dentinal walls using a scanning electron microscope (SEM). This smear layer was composed of dentin, pulp and bacterial remnants. The authors stated that “most standard instrumentation techniques produced a canal wall that was smeared and packed with debris.” In 1984 Pashely described the smear layer as being composed of two phases; an organic phase, composed of collagen residues and glycosaminoglycans from extracellular matrix of pulp cells, which acts as a matrix for an inorganic phase. This