The 1919 edition makes no reference to revision to the text so they may be identical. Relation of social psychology to sociology proper. A common environment or experience does not produce social planes. Race traits are not social planes. Such planes arise from interactions.
Social psychology explains both society and the individual.
How planes of sentiment regarding slavery formed. Factors in the formation of religious planes. Imitation vs. Affinity. The higher psychic growths imply association. Much of one's mental content comes from others.