Under the prevailing cool conditions, water is very widely sufficient in the Arctic for such limited growth as the climate, etc., allows, and the main vegetational differences in any particular belt are rather in accordance with the actual habitats. Thus local edaphic or physiographic variations can ring the most immediate and fundamental changes in the local plant life. On the other hand a progressive and almost regular over-all depauperation of the vegetation is to be observed as we go farther and farther north; and as this tends to be rather closely comparable in the various sectors, it is deemed expedient to separate each sector (and consequently the Arctic as a whole) roughly into three main belts. These are the low-Arctic, in which the vegetation is continuous over most areas, the middle-Arctic, in which it is still sufficient to be widely evident from a distance, covering most lowlands, and the high-Arctic, in which closed vegetation is limited to the most favourable habitats and is rarely at all extensive. The following outline account of the main vegetational types of the Arctic will accordingly have, under each major heading, some consideration of the expression of this type in each of these three belts, ranging from south to north. Examples of low-arctic lands are the southern portions of almost all sectors, of middle-arctic lands Jan Mayen Island and the vicinity of Point Barrow, Alaska, and of high-arctic lands the whole of the Spitsbergen Archipelago, and the Canadian Eastern Arctic north of Lancaster Sound.