fertilization (noun, pl. fertilizations) – the fusion of sexual cells (gametes or entire gametangia) with one another. Fertilization in ascomycetes (as in most other fungi) is a two-step process. The fusion of sexual cells (gametes or entire gametangia) typically results only in plasmogamy. The cytoplasm merges, but the two nuclei remain intact, often for considerable time. The presence of two haploid nuclei within the same cell is called a dikaryon and hyphae formed by these cells are therefore dikaryotic hyphae. karyogamy, i. e., the fusion of the nuclei within a dikaryotic hypha, takes place only shortly before ascospore formation. Ascospores are then formed as a result of free cell formation and the enveloping membrane system (= EMS).