types come together and fuse. In some fungi the fusion of two haploid cells immediately results in diploid cells (2n). However, in other fungi (ascomycetes and basidiomycetes), an intervening dikaryotic stage (n + n, i.e., two nuclei per cell) occurs; such a condition is called a dikaryon and the phase is called dikaryophase of fungus. Later, the parental nuclei fuse and the cells become diploid.
The fungi form fruiting bodies in which reduction division occurs, leading to formation of haploid spores. The morphology of the mycelium, mode of spore formation and fruiting bodies form the basis for the division of the kingdom into various classes. . .
Phycomycetes Members of phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants. The mycelium is aseptate and coenocytic. Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). These spores are endogenously produced in sporangium.
A zygospore is formed by fusion of two gametes. These gametes are similar in morphology (isogamous) or dissimilar (anisogamous or oogamous). Some common examples are Mucor (Figure .5a) , Rhizopus (the bread mould mentioned earlier) and Albugo (the parasitic fungi on mustard). .
. Ascomycetes Commonly known as sac-fungi, the ascomycetes are mostly multicellular, e.g., Penicillium , or rarely unicellular, e.g., yeast ( Saccharomyces ) . They are saprophytic, decomposers, parasitic or coprophilous (growing on dung). Mycelium Figure .
Fungi: (a) Mucor (b) Aspergillus (c) Agaricus (c) (a) (b) is branched and septate. The asexual spores are conidia produced exogenously on the special mycelium called conidiophores. Conidia on germination produce mycelium. Sexual spores are called ascospores which are produced endogenously in sac like asci (singular ascus).
These asci are arranged in different types of fruiting bodies called ascocarps. Some examples are Aspergillus (Figure .5b) , Claviceps and Neurospora. Neurospora is used extensively in biochemical and genetic work. Many members like morels and truffles are edible and are considered delicacies.
. . Basidiomycetes Commonly known forms of basidiomycetes are mushrooms, bracket fungi or puffballs. They grow in soil, on logs and tree stumps and in living plant bodies