The mechanism of the carpospore liberation under different osmotic condtions was studied, Results of experiments are as follows: 1. A decrease in the osmotic concentration of the external solutions increases the ratio of spore shed cystocarp(Fig. 1). Only when cystocarps are bathed into hypotonic solution of calcium chloride, the effect of the acceleration is scarecely detectable. 2. The spore liberation from cystocarps occurs when the thallus is immersed into natural sea water after the drying in shaded place. But this ratio of spore shed cystocarp increases more effective in such a solution isotonic with natural sea water as glycerol, potassium chloride and sucrose than in natural sea water(Table 2). The marked antagonism is also observed between pairs like CaCl2 and KCl, CaCl2 and NaCl, CaCl2 and sucrose(Fig. 2). 3. By the transfer to solutions isotonic with sea water after dipplng in hypertonic ones, spore shed cystocarps increase in number(Fig. 3). 4. Spore diameter increases in hypotonic solutions, especially of potassium chloride, sucrose and glycerol(Table 4). 5. Algal bodies elongate also in hypotonic solutions, but the ratio is not so much as the case of spores(Table 4). 6. Spore liberation from the denuded spore assembly (nucleus) is accelerated even in isotonic solutions of sucrose, KCl, glycerol etc. From these results, it is concluded that the change of the osmotic concentration of external solutions has a significant effect of inducing carpospore liberation in Gracilaria verrucosa. It seems, therefore, that expansion of spores results in an increment of inner pressure sufficient to cause the liberation from carpostome.