Rice plants were grown in nutrient solutions containing 0.5, 20, and 500 ppm of calcium as CaO. Microscopic observation revealed that the mesophyll structure in the leaves was disordered at the lowest Ca level and became healthy with increasing supply of calcium in the culture solution. The chemical constitution of cell wall and the composition of sugar in each chemical constituent of wall differed little among the leaves grown with different levels of calcium. The calcium contents in the walls of calcium deficient leaves were extremely low as compared with those of normal leaves. The amount of calcium extractable in the lignin fraction of Ca 0.5 leaves was only about one-sixth of that of Ca 500 leaves. Furthermore, calcium in the lignin fraction was leached out by treating the wall previously with 2acetic acid solution. These results suggest a close association of calcium with ligneous substances in combined forms of physiological importance in the cell walls.
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