Systematic studies on phylloplane microorganisms are required to answer questions concerning pathogenic and saprophytic destruction of leaves.Pisumleaves, which are excellent experimental material, have been examined during the entire growing season of the plants, and beyond, in the first stages of decomposition. Green leaves were not extensively colonized by filamentous fungi. At the onset of senescence, a dramatic increase was observed in the activities of several saprophytes and on newly dead leaves colonization proceeded even more quickly.Cladosporium, Stemphylium, andAlternariawere frequently observed in the first wave of saprophytes. The first two genera sporulated soon after the leaves died. The increase in saprophyte activity was considered to be primarily a result of alterations in leaf physiology though the possibly beneficial influence of changes in various climatic factors may not be neglected.
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