Thirty-two colony variants were obtained from the two different strains of Bacterium malvacearum which were isolated from the angular spots of cotton at Taihoku, viz. 9 variants (A-I in fig. 1) from culture strain 427 and 23 variants (A-W in pl. II) from culture strain 450. All the variants derived from the former are resistant to the phage which was isolated from the diseased leaves by MATSUMOTO and HUZIOKA, (4) while any of the latter are susceptible to it, though somewhat different in susceptibility and size. of plaque produced, generally more susceptible variants producing larger plaques (table 6). The plaques produced on the cultures of variants E, J, and M enlarge to a great extent with the increase of the incubation period (table 6). The phage in question proved to be consisted of at least two elemental phages. The one is active against all the variants, and the other is only active against those except E, J, M, O, and P variants (tables 7-8). The size and number of plaques are more or less decreased with the increase of the amount of bacteria used (table 11). The same is true with the temperature within a certain limit, although in this case the effect is more remarkable on the number of plaques. Resistant strains developed from the phage-bacterial cultures are not apparently different in morphological characters from their original susceptible bacteria.