Studying the influences of the aqueous solution of KCl and other seven kinds of the neutral salts and the hydrogen ion on the duration of life of the spermatozoid of Athyrium melanolepis Christ and other six species of Pteridophyta, the following facts were known.
1. The duration of life of the spermatozoid is effected by the cation and the more the ion-value of cation increases, the more the limit concentration of the solution in which the spermatozoid lives decrease gradually.
2. The hydrogen ion disturbs the duration of life of the spermatozoid. The medium whose acidity is alkaline (pH 8.2) is most favorable for the duration of life of the spermatozoid.
3. In fertilization, when the spermatozoids approach to the archegonium and enter in it and at last reach the egg-cell, it is favorable that the ion-value of cation in the medium is small and the acidity of medium is alkaline, in which the spermatozoids move on. This fact is significant and important from the viewpoint of the physiology of fertilization.