الفهرس 
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Abstract
The objective of the research work presented in this thesis were to study the occurrence and structure of fungi in two biological systems, namely; the River Nile and the gravel hyDROPonics system (GBH). The River Nile particularly the Damietta branch, is a distinctive ecosystem that provides a range of substrata for microorganisms, including various kinds of vascular plants on its banks, aquatic macrophytes such as reeds and free floating vegetation. This study aimed at investigation of the occurrence of fungi at 34 samples sites with an amended investigation of the seasonal occurrence at six selected sites.