The following scheme is given: (1) Well drained, heavier soils[long dash]plceeta hylocomiosa; (2) insufficiently drained, heavier soils[long dash]P. polytrichosa; (3) stagnant swamps[long dash]P. sphagnosa; (4) swamps with surface drainage[long dash]P. herbosa; and (5) well drained, heavy, somewhat calcareous soils[long dash]P. fruticosa. Each group includes several plant communities, as follows. Group 1: (a) plceetum oxalidosum on the best, well drained soils; (b) P. atragenoso-oxalidosum and (c) P. polystichosum, both on fair or good heavier soils; (d) P. myrtillosum on somewhat inferior, moister soils; (e) P. empetroso-vacciniosum on drier and poorer soils. Group 2: (a) P. polytrichosum on poorer, moister soils; (b) P. empetroso-polytrichosum on moist podsol soils. Group 3: (a) P. sphagnosum on shallow moss peat; (b) P. caricoso-sphagnosum on deep peat with a high water table. Group 4: (a) P. fontinalc on fairly well drained and rich soils subject to over-flow; (b) P. sphagnoso-herbosum on poorer muck soils with a slow run-off. Group 5: (a) P. tiliosum on fairly good, somewhat sandy soils with a portion of calcareous material; (b) P. quercoso-tiliosum, on the richest soils, often underlain by limestone and marl. Three fundamental ecological or successional series are recognized: (1) plceeta hylocomiosa[long dash]P. polytrichosa[long dash]P. sphagnosa; (2) P. hylocomiosa[long dash]P. herbosa; (3) P. hylocomiosa[long dash]P. fruticosa. The succession of the first two series is affected by the differences in moisture content, degree of stagnation, oxygen supply, and availability of plant food, while the succession of the latter series is affected entirely by the availability of mineral nutrients. Besides the changes of soil, the climate and influence of plant community itself are responsible for the succession outlined.