They become decoupled from the main annulus and don't come back," he added.

Some years ago, Corus developed the 'pipe in pipe' - an inner pipe with an annulus between that and the outer sleeve that insulates the emerging oil against sea temperatures which can slow the flow.

Each of 248 species is illustrated with an excellent color photograph (which almost always shows both the tops and the undersides of sample fungi), and its cap, gills, stalk, and annulus are all described in meticulous detail, along with information with regard to where each species is most likely to be seen, and its edible or toxic characteristics.