The period during which American pomology may be said to have been in the hands of wealthy amateurs began shortly after the close of the Revolution and did not fully merge into that of commercial pomology until the close of the Civil War. Soon after the beginning of the Nineteenth Century, horticulture, in fact all agriculture, was greatly stimulated by the publication of agricultural books[32] and magazines[33] and the formation of agricultural and horticultural societies.[34] The frequency of the names of these publications of a century ago in _The Plums of New York_ is an indication of the contributions they made to the culture of the plum. Having briefly outlined the history of the Domestica plums, we come now to a discussion of what we have under cultivation in this fruit. The Domestica plums, 950 or more mentioned in this text, may be divided into several more or less distinct pomological groups. These groups are of interest because in their history the evolution of the plum under consideration is further developed; because such groups are serviceable to plum-growers, as each division has adaptation for particular conditions or particular purposes; and because of their value to the breeder of plums since the largest and best differentiated groups, as a rule, have their characters most strongly fixed and may be relied upon to best transmit them to their offspring. Groups of plums in pomology are founded for most part upon the characters of the fruit since these are most readily recognized by fruit-growers. Yet whenever possible, leaf, flower and tree-characters are considered. The name given is usually that of the best known variety in the group though in some of the divisions the name is that of the variety which seems to be intermediate in character between the other members of the group. The groups of plums recognized by pomologists were far more distinct as we go back in their history. For, in the past, each fruit-growing region had a pomology of its own in which the varieties of any fruit were few and similar, constituting but one, or at most a very few types. The various groups of plums, therefore, largely represent distinct plum-growing regions. With the increase in intercourse between the countries of the world, cultivated plums have been taken from place to place and as new varieties have originated, often from crosses between varieties, the dividing lines between divisions have been more or less broken down. The first of the groups to be considered is:—