(1) In staining the protoplasms in root cells of crops which are more susceptible to soil acidity, positively charged dyes such as methylene blue and methyl violet stained more deeply, but negatively charged dyes such as eosin and bordeaux red stained in faint. In mature crops, the dyeing was influenced by the rate of content of cytoplasmic protein. Little relation was found between the degree of staining of the epidermal layer cells and the tolerance of crops to soil acidity. (2) For the estimation of the tolerance of crop plants to highly acidic soils using roots of young crops by measuring the absorbability of Al, the following technique was found to be suitable: cross sections of 0.2 mm in thickness which were obtained at about 15∼18 mm from the root tip, were pretreated with 0.03M KCN for 5 minutes after shutting up in a brass net of 80 mesh, then immersed in N/1, 000 AlCl₃ of pH 5 for one hour. The treated materials were rinsed in distilled water for 5 minutes and soaked in a mixture of equal amount of 0.1% aluminon and 3N ammonium acetate for 70 minutes, then finally immersed in Clark-Lubs (c) buffer solusion of pH 5 for 10 minutes. Before, soaking in each new solution wire gauze was wiped thoroughly with filter-paper. Observation of red staining of cytoplasms was made in a drop of the last buffer solution on a slide glass under a microscope at a magnification of 50×approximately. (3) The amount of Ca absorbed by 1g. cytoplasmic protein of the roots of crops which are tolerant to highly acidic volcanic ash soil in each medium at pH 6, pH 4 or pH 6-pH 4 was lower than that of non-tolerant one, though a little less at pH 4. The root of young crops exceeded in the amount of Ca absorbed by 1g. cytoplasmic protein to that of the matured one. (4) The proportion of cytoplasmic protein in the root cell was higher at younger stages than that of the matured, though the percentages of the protein contents at both stages were found to correlate to the lime requirement of the crops. (5) If the amount of Ca absorbed by cytoplasmic protein of the root of 100 g. in dry weight is given by the formula of (Ca uptake by 1g. cytoplasmic protein in root)×(percentage of cytoplasmic protein in root) and Ca refer to the cation examined, the amounts of Ca absorption of the root estimated by means of this formula show high correlation to lime requirement or Ca percentage in the root of water culture. In case of Al, owing to this formula, the amount of Al absorbed in the root also correlates to the yield ratio on the highly acidic volcanic ash soil.