The need for ecological data on ferns is becoming increasingly apparent as more effort is directed toward an understanding of the significance of their morphological and physiological diversity (Wagner, 1973). If detailed ecological studies of fern sporophytes have to date been too few, such studies on the gametophyte generation are almost non-existent. The reproductive cycle of ferns has been known for over a century, and more than a thousand articles on fern gametophytes have been published, half of these in the last quarter century (Miller, 1968; Nif, 1975; Nayar & Kaur, 1971). However, nearly all data on gametophyte growth and sexual reproduction have been based on laboratory observations. Several factors have contributed to this paucity of information on gametophyte ecology, but perhaps the most important has been a widely held notion that gametophytes cannot be found in nature, or if found, cannot be identified. Several recent studies have indicated to the contrary, that in situ gametophyte studies not only are feasible, but that they are essential for the integration of existing laboratory data into studies on the natural history of ferns (Cousens, 1973; Holbrook-Walker & Lloyd, 1973; Lloyd, 1974; Farrar & Gooch, 1975). To investigate further the feasibility of studying fern gametophytes in nature, we have begun a long-term observational study of fern reproduction in Woodman Hollow, a relatively isolated canyon in central Iowa, in which 13 species and 11 genera of ferns occur (see Table 1). This study is designed to answer the following questions. When are spores available for germination? When and where does reproduction occur and how is it influenced by microand macroclimates? When and by what breeding systems are sporophytes produced? Does sexual reproduction occur in nature on a regular basis for all species? Results of the first year of study (Farrar & Gooch, 1975) indicate that the data needed to answer these and other questions will be forthcoming. Here we report some unexpected data relevant to the question of when spores are available for germination. Observations made on the time of spore maturation and first release during the growing season gave results which were similar to those of Hill and Wagner (1974) for pteridophytes in Michigan. Differences found in the two studies were no greater than might be expected due to differences in latitude, climate, habitat, and seasonal variation. Our observations also support their estimate that most spores of a given species are released during a period of about two weeks. However, a two week period of maximum release, if taken as a guide to the duration of spore release, may be very misleading. Our observations at Woodman Hollow indicate that for most species, significant quantities of spores are retained on the fronds after the initial release period and may be dispersed during a much longer period. Only in Botrychium virginianum and Osmunda claytoniana were essentially all