Contribution of fern gametophytes to the growth of produced sporophytes on the basis of carbon gain

Sporophytes appeared on most gametophytes of Thelypteris palustris (Salisb.) Schott that reached a certain size, which is interpreted to be a critical size of gametophytes for the production of sporophytes. After sporophytes were produced, attached gametophytes ceased dry weight growth, but the gametophytes which did not produce sporophytes grew successively. It was hypothesized that matter produced by gametophytes was being supplied to young sporophytes. Photosynthesis and respiration of gametophytes with attached sporophytes were not significantly different from that of gametophytes without sporophytes. Photosynthetic activity of gametophytes dropped from 0.18 to 0.03 mol CO₂ g^–1 s^–1 during the growth period. The higher photosynthetic rates of gametophytes in the early growth stage were important for reaching the critical size for sporophyte production in a short time. Sporophytes in the one leaf stage averaged 0.14 mol CO₂ g^–1 s^–1 of photosynthetic activity. The results show that sporophytes that had expanded the first leaf grow by their own photosynthetic production. Gametophytes allocated the photosynthate for sporophytes and it was an important aid before the one-leaf stage. The supportive role of gametophytes ended at that stage.