Which one of the following is not a criterion for classification of fungi?

The correct option is Mode of nutrition.

Fungi are classified into various classes (such as Phycomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes) based on specific morphological and reproductive characteristics. Let's analyze the criteria used for this classification:
1. Morphology of mycelium: The structure of the mycelium (whether it is aseptate and coenocytic, or septate and branched) is a primary criterion for classifying fungi.
2. Mode of spore formation: The types of spores produced (asexual or sexual) and how they are formed (endogenously or exogenously) are key classification criteria.
3. Fruiting bodies: The type and structure of the fruiting bodies (such as ascocarps in Ascomycetes or basidiocarps in Basidiomycetes) are also crucial classification features.

In contrast, the mode of nutrition is not used as a criterion for classifying fungi into these different classes because almost all fungi share a common heterotrophic mode of nutrition (being saprophytic, parasitic, or symbiotic). Therefore, it does not serve as a distinguishing feature for classification within the kingdom Fungi.