In order to investigate the mechanism of spore attachment in red algae, some observations and experiments were conducted. As the material, Polysiphonia japonica Harvey was chosen chiefly because of the following reasons; 1) Polysiphonia produces comparatively large spores which have the advantage of being closely observed through a microscope with a high-power objective, 2) this alga is available for such a long period in winter as repeated trials are possible, 3) since this is epiphytic to develop in abundance on some intertidal species of Sargassum, it is easy to obtain the material. Carpospores are preferable to tetraspores, for it is not necessary to examine material with a microscope whether it is sterile or not. A small glass vessel of 5×8×2.5 cm was made, and for one of its planes a thin glass plate of 5×8 cm, 0.13 -0.17 mm in thickness, was used so as to observe the inside spores horizontally. 1) Spores sink at an average speed of 93 μ/sec, that is 10.8 sec/mm. Though this speed is the fastest example among the reported ones, it is still slow enough to take time to reach a substratum. 2) When sinking spores touched the slide glass with a 45°-angle of slope, no spores were observed that adhered immediately, but they moved down instead. Moving progress of each spore was successfully observed with 7 instances, and time, distance, and speed were recorded. They usually moved down sliding, but sometimes rolling. Besides, 36 more instances were measured in which the moving of spores was not observed in succession from the beginning to the end. On many occasions spores moved down at a speed of approximately 1mm/min, but the speed was variable in each spore and even the same spore changed the speed irregularly. In most cases the range of speed was about between 0.5 and 1.5 mm/min, and here are two records with the longest time and distance confirmed; 7.2 mm in 18.9 minutes, 11.5 mm in 8.5 minutes. 3) The slide glass mentioned above was slid along its direction for 1 cm and back at different speeds 5 minutes after the spore stopped. In the case of a 10 mm/sec speed, no spores remained, but in the case of a 1 mm/sec, each one was still observed at its place. Since there are only a few results available, it can follow that some spores may settle on the glass in the stiring water with the speed of more than 10 mm/sec. 4) A slide glass was placed horizontally and was moved along its direction or vertically at the speed of 1 cm/sec at different interval after each spore touched it. Even in the case when the glass was moved just after a spore touched it, the spore remained there at a high rate. It is evident that the spores are embedded in mucilage which is released together with the spores.