In A Book that concentrates chiefly upon terrestrial communities and can at most give only an outline of the characters of some of these, it is not practicable to allot an equally large space to aquatic communities, for many of which there are in any case special books and monographs. However, the interspersion together of land habitats and water bodies is part of the whole pattern and needs some mention. There are the rich Transition habitats of marsh and the riparian zone that unite the two, while the flow of water systems influences even more fundamentally the soils and microclimates of land habitats. The water bodies and marshes of woodland have received comparatively little attention. This has happened partly because many of these waters lack green plants and so have not entered directly into the surveys of plant ecologists. Also many of them look unattractive to the naturalist or appear small and unimportant features of a wood. Wytham Woods has an exceptionally rich profusion of springs, spring flushes, marshes and streams which I will now try to fit into the general pattern of habitats already described.