(There is a direct connection between purely aquatic vegetation, or those types of plants that live in water, wholly submerged or floating, or partly submerged, through the last, or the reed swamp, with that marginal vegetation which consists of marsh vegetation, the fen formation, ordinary wet meadows such as rush associations, or even lowland moors or bogs. Hence some proportion of the plants selected for inclusion in this section (more particularly included in those which are found in wet places) are of this last type, or paludal, and not of purely aquatic or lacustral type, though occasionally purely aquatic. In the same way some water plants become terrestrial, by reason of change in the water-level.)