Why did I decide to write this book? As an undergraduate student I could not make up my mind whether I wanted to be a zoologist or a botanist, so I decided to adopt ecology, in its broadest sense, as my area of interest. This led me to think about interactions among organisms and to try to look at ecosystems from a holistic, rather than from an autecological, point of view. As someone with little formal training in mycology, my interest in fungi started during my doctoral research, especially when attending university-wide lectures by C. T. Ingold,.