Spore germination of five globally threatened fern species [Culcita macrocarpa C. Presl, Dryopteris aemula (Aiton) O. Kuntze, D. corleyi Fraser-Jenkins, D. guanchica Gibby and Jermy and Woodwardia radicans (L.) Sm.] was determined after 1, 6 or 12 months of storage in glass vials (dry storage) or on agar (wet storage) at -20, 5 or 20 degrees C. In all species, storage technique, storage temperature and the technique-temperature interaction all had a significant effect on germination percentage. In most cases, the germination percentage was best maintained by wet storage at 5 or 20 degrees C. In the case of the hygrophilous species C. macrocarpa and W. radicans, 6 or 12 months' dry storage killed most spores. Only Woodwardia radicans germinated in the dark during wet storage at 20 degrees C. Wet storage at 5 degrees C prevented dark germination, and reduced bacterial and fungal contamination. Wet storage at -20 degrees C killed all or most spores in all species. In the three Dryopteris species, the differences among the storage conditions tested were smaller than in C. macrocarpa and W. radicans, and the decline in spore viability during storage was less marked, with high germination percentages being observed after 12 months of dry storage at all three temperatures. Dry storage, which has lower preparation time and space requirements than wet storage, was generally more effective at the lower temperatures (-20 or 5 degrees C).

The gametophytic generation of the allotetraploid Polystichum aculeatum and its diploid parents, Polystichum setiferum and Polystichum lonchitis, was studied in order to compare their morphology, gametangial ontogeny, and breeding system. Six populations, two of each species, were selected for spore collection. Germination, gender expression, and antheridiogen experiments were established on agar and soil culture media. Germination percentage in the tetraploid was higher, and the only morphological difference was found in the length of marginal hairs that were also longer in P. aculeatum. Gender expression in the allotetraploid was a mixture of the diploids. Differences in gender expression of both diploids, with many male prothalli in P. lonchitis and many female ones in P. setiferum, may favor the formation of the hybrid that originated the allotetraploid. An antheridiogen system was observed in both P. aculeatum and P. setiferum, and each species responded to one another's antheridiogen. In contrast, exudates from P. lonchitis failed to induce precocious maleness within the species but did induce an antheridiogen response in gametophytes of P. setiferum.

Environmental sex determination is present in several animal and plant lineages, in which gender depends on diverse factors such as temperature, light and water availability. This study examines effects of water availability and pheromones on the production of female and male organs by three fern species adapted to dry habitats. Isolated individuals become first female and then bisexual, irrespective of the degree of soil moisture, and, consequently, may self-fertilize. However, female individuals release pheromones that induce maleness in nearby individuals, thus favouring cross-fertilization.

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to study the germination capacity of Cryptogramma crispa, spores were cul-'etri dishes with nutritive medium solidified with agar. Germination was and 25°C, and, as in most of homosporous ferns, the germination optunurr bove 20°C. Two light intensities were used, 10 and 40 jjuEm -^ -1 , to reproduce le spores falling on open sites or in rock cracks or hollows. A lower light germination. After sowing, some plates were kept at chilling and other alIn the Iberian Peninsula (Spain and Portugal), Cryptogramma crispa R. Br. grows on ecologically very particular and well defined habitats. It occupies especially siliceous stone fields, such as granite, gneiss, sandstones, quartzites, or slates in high mountain zones, usually above the timber-line. In the Iberian Peninsula, its optimum is about 2000 m. The plants grow preferentially in rock fissures or cracks and in hollows between rock blocks. In these habitats, which are mostly over 2000 m elevation, the growing season may be very short, scarcely two months in extreme conditions, and usually no more than four months (Rivas-Martinez, 1987). The considerations of the distribution of pteridophytes suggest the need for more detailed investigations on the life-cycles of species to determine the importance of specific variations in the life-cycle in limiting the distributions of plants. Variations in the distributions of species might be accounted for by random processes, such as dispersal, or in a more deterministic manner by subtle and specific variations in life cycle characteristics (Woodward, 1987).In ferns, it is important to study the factors that can affect the development of the gametophyte that would lead to the establishment of the sporophytic gen-Probably due to the short period to complete their development, C. crispa sporophytes reach the end of the summer with practically all the spores still retained (Peck et al., 1990; pers. obs.), which are released at about the same time that the leaves shed. Thus, the spores are released at the end of the growing season.It is difficult to reproduce wild conditions in short-term laboratory experiments. But some climate changes, especially temperature ones, that may influence spore germination can be tested in the laboratory, provided that in nature conditions may be operating over a longer period. Thus, a few experiments

Unisexuality, promoted by non-specific antheridiogens, enhances random mating both within and among species. The resulting hybridization can favour the reproductive exclusion of the allopolyploid in sites where it is outnumbered by diploids. However, the earlier production of gametangia in the allotetraploid favours assortative mating and may thus counterbalance reproductive exclusion.

Studies on genetic diversity help us to unveil the evolutionary processes of species and populations and can explain several traits of diploid-polyploid complexes such as their distributions, their breeding systems, and the origin of polyploids. We examined the allozyme variation of Dryopteris aemula and D. oreades, diploid ferns with highly fragmented habitats, and the allotetraploid D. corleyi to (1) analyze the putative relationship between both diploids and the tetraploid, (2) compare the levels of genetic variation among species and determine their causes, and (3) assess the breeding system of these taxa. The allozymic pattern of D. corleyi confirms that it derived from D. aemula and D. oreades. The lack of genetic diversity in D. aemula, a species of lowland habitats, may be due to genetic drift associated with the contraction of populations in the last glaciation. By contrast, the alpine D. oreades had moderate intrapopulation genetic variation, which may derive from the expansion of populations during the last glaciation. In the latter species, low interpopulational variation suggested effective gene flow (spore exchange), and genotype frequencies in Hardy-Weinberg equilibrium indicated cross-fertilization of gametophytes. Evolutionary history appears to be an essential element in the interpretation of genetic variation of highly fragmented populations.

Spore germination of Culcita macrocarpa C. Presl and Woodwardia radicans (L.) Sm. from nine populations at the northern limit of their distribution, in the northwest Iberian Peninsula, was investigated. In a first experiment, population type and temperature (10, 15, 20, and 25 °C) were both found to affect germination percentage and germination time significantly in both species. There were also significant interactions between the two factors with respect to the percentage germination of C. macrocarpa and the germination time of W. radicans. In C. macrocarpa there was an outstanding increase in germination time at 15 °C and, above all, at 10 °C, whereas in W. radicans the most remarkable result was the existence of two populations with especially low germination percentages. In a second experiment, germination of 20 individuals from each population of W. radicans was compared with similar inter‐population differentiation. Although its variability possibly has a genetic basis, these species are able to germinate successfully, and it seems probable that the season in which it occurs depends more on spore release than on thermal conditions in the populations. The effect of temperature on germination in both species does not explain their coastal distribution. Temperature is probably more important in limiting other stages of the life cycle.