There has been little information on the relation of rootstocks to the occurrence of the“rough bark disease”of apple trees except for some studies carried out in our laboratory. In particular, no literature has been available on the manganese absorption by rootstocks, despite the importance of this problem in elucidating the cause of this disease. In a previous paper (AOKI, 1966), pot experiments were undertaken by using the soil taken from an orchard where the trees were severely affected by the disorder. It was found from this study that the two kinds of rootstocks, Malus sieboldii and M. pruniforia differed conspicuously in their manganese content. The former contained much larger amount of this substance in its leaves and twigs than the latter. It was therefore assumed that there might be a considerable difference in the ability to absorb manganese between the two rootstock plants.<br>In order to substantiate this assumption, experiments were began by using a method of sand culture. in 1965 Two-year-old seedlings of Malus sieboldii, M. pruniforia and Jonathan apple were thus planted in pots of river sand. Culture solution, which contained manganese in concentrations of 0.5ppm and 30ppm respectively, were pored every two days from the beginning of May to the first part of September, and the manganese contents of all seedlings were examined in relation to the manganese level of the culture solutions. The results are summarized as follows:<br>1. All the three kinds of seedlings showed greater concentrations of manganese in every portion of their body in the 30ppm manganese lot than in the 0.5ppm one.<br>2. In both lots, M. sieboldii had the largest amount of manganese in the leaves, current shoots, twigs of preceeding year and main roots. Jonathan seedlings were next and M. pruniforia showed the lowest level of manganese content. The difference between M. sieboldii and M. pruniforia was most conspicuous and proved to be highly significant by statistical test.<br>3. In fibrous roots, on the other hand, M. sieboldii had the smallest amount of manganese among the three kinds. Manganese content was abnormally high in the 30ppm cultures of M. pruniforia and Jonathan, making a sharp contrast with that of M. sieboldii. This suggests that the active uptake and subsequent accumlation of manganese ion in fibrous roots took place in M. pruniforia and Jonathan seedlings.<br>4. Since fibrous roots are responsible for absorbing water and other nutrient material, the difference in manganese content of plant portions other than fibrous roots among the different seedlings can not be attributed to their different ability to absorb manganese ion. Some other factor or factors might be responsible for this. This is an important point to be studied further and discussed to a certain extent in this paper.