The fine structures of the spore walls of Frullania (Hepaticae), representing 3 subgenera, Trachycolea, Homotropantha and Frullania, were investigated by electron microscope. The results are as follows : 1. No distinct difference could be seen in the size, external shape, color and thickness of the exine of the spores in these 4 species. 2. The number of foramina on a diameter was generally the same in the 4 species. The diameter of the foramina on an average were (in size order) F. fauriana (4.29μ), F. nishiyamensis (5.53μ), F. nodulosa (6.26μ) and F. tamarisci ssp. Moniliata (8.3μ). 3. The foramina was hollowed in F.fauriana and F.nishiyamensis. But the foramina was nipple like (scallopped in profile view) in F. nodulosa and F. tamarisci ssp.moniliata. 4. The circumference of the foramina and the sections between each foramina were densely covered with numerous, irregularly tortuous protuberances in F. fauriana, while those of the other 3 species were densely covered with numerous minute mamillae. 5. The foramina was covered by the irregularly tortuous protuberances and minute mamillae in F. fauriana. In surface view, those of F. nodulosa and F. tamarisci ssp.moniliata were covered by many spinous protuberances and those of F. nishiyamensis were covered by both spinous protuberances and mamillae. 6. The spinous protuberances covering the foramina were 25 (35) 40 in number and arranged in 2-4 cocentric circles in F. nodulosa, while in F. tamarisci ssp.moniliata, it was 8-12 in number in a cocentric circle. As mentioned above, the characteristics of the fine structures of the spore wall in these 4 species of Frullania representing 3 subgenera could each be distinguished clearly by electron-microscopic observation. Therefore, it seems that the characteristics of the fine structures of the spore wall may be one of the important taxonomic feature not only between species but also between sections or subgenera.
