The genus Prunus is without peer in the number of distinct, natural, esculent products it furnishes man. Here belong the stone-fruits--peaches, plums, cherries, almonds and apricots, represented by some forty edible species, which, through long domestication, have been broken up into not less than 5000 orchard-varieties, of which at least 3000 are now under cultivation. Of the two-score cultivated species of this genus, _Prunus persica_, the common peach, is easily the most remarkable when judged either by the senses which make foods palatable and pleasant or by the criteria that establish the commercial worth of a product. As virtues which give the peach leading place among stone-fruits, we may specify: Wider distribution and consequently commoner cultivation and a greater number of varieties; larger size, greater beauty, pleasanter and more diversified taste, and more culinary uses than other stone-fruits; and greater productiveness, more rapid growth and earlier fruiting of the trees than most of the species of the genus. The place of the peach in the genus Prunus is thus easily established from a horticultural point of view, but it is a much more difficult matter to make clear its botanical standing among the species with which it is considered botanically related. The botanical relations of the several stone-fruits to each other have been set forth in the foregoing books of this series on plums and cherries, but, for the convenience of those who may not have these treatises, a summary of the relationships of the species of Prunus is presented. Besides, greater emphasis on several differences between the peach and its congeners is needed. In particular, since some notable naturalists have held that the peach is a modified almond, the differences between these two fruits must be more clearly set forth. Nearly every botanist who has done much towards classifying plants has grouped the stone-fruits according to a plan of his own and there are, therefore, many classification schemes and consequently a most confused nomenclature for this genus. Happily, the pitfalls in synonomy dug by botanists need not worry horticulturists; for each of the stone-fruits constitutes a distinct horticultural group. In tree or fruit of peach, plum, cherry, apricot, or almond, who could mistake one for another? For horticultural purposes we accept as best one of the oldest and yet one of the most commonly used classifications which places in one genus all of the stone-fruits. What are the lines of cleavage between the several stone-fruits of common cultivation?