1983 年 33 巻 2 号 p. 161-167
In the leafy phenology of ferns native to Hokkaido, there are summer-green, semi-evergreen, evergreen and winter-green types. Among them, summer-green is the predominant one in Hokkaido, the northern most island in Japan. Ferns such as Adiantum pedatum, Dryopteris austriaca and Woodsia polystichoides are typical summer-green ferns whose leavers unfold from late May to June and decay during October in the mature sporophyte. However, the leaves of young sporophytes can behave as if they were evergreens. In order to evaluate the stage of changing from evergreen-like to summer-green in the young sporophytes of summer-green ferns, the number of venation of the leaves (number of veins branching from the midrib) was used as a quantitative expression of the developmental age of the sporophytes. The maximal number of venation (NV) of the mature sporophytic leaf was 86 in W. polystichoides ; 60 in D. austriaca and 69 in A. pedatum. At the foot of Mt. Teine near Sapporo, the maximal NV of the young sporophytic leaves with greenness in winter was as follows : the first was 27,the second 28 and the third 35. The relative developmental age of NV of young leaves with greenness in winter to the maximal NV of mature leaves was 0.314,0.467 and 0.493 respectively. It was postulated that the summer-green characteristic is one of the adaptations to a cool climate in Japan, W. polystichoides was considered to be the most adaptive fern among the three summer-green ferns of Hokkaido.