The stone of the plum is usually compressed, longer than broad, smooth or roughened, thickish and with an acute margin along the ventral suture and thinnish or grooved on the dorsal suture. The stone of the cherry is usually globular, always much thickened, smooth or a very little roughened, ridged and grooved on the ventral suture, with a thin, scarcely raised sharp margin on the dorsal suture. The stone of the apricot is similar to that of the plum though thicker walled, with a more conspicuous winged margin, and is sometimes pitted. The stone of the peach is compressed, usually with very thick walls, much roughened and deeply pitted. In the almond the stone resembles in general characters the peach-stone, but all almond shells are more or less porous and often fibrous on the inner surfaces. The stone is the part for which the almond is cultivated and is most variable, the chief differences being that some have thick hard shells and others thin soft shells. The leaves of plums are convolute, or rolled up, in the bud. Cherry, peach and almond leaves are conduplicate, that is are folded lengthwise along the midrib in bud while the leaves of the apricot, like those of the plum, are convolute. The manner in which the leaves are packed in the bud is a fine mark of distinction in stone-fruits. In size and shape of leaves, as well as in the finer marks of these organs, the botanist and pomologist find much to aid in distinguishing species and varieties but little that holds in separating the sub-genera. The last statement holds true with the floral organs also. The near affinity of the stone-fruits is further shown by the fact that plums and apricots, plums and cherries, and the several species of each of the distinct fruits inter-hybridize without much difficulty. It is a fact well-known that hybrids often surpass their parents in vigor of plant and in productiveness and this has proved true with most of the hybrids in Prunus of which we have accounts, thereby giving promise of improved forms of these plants through hybridizing. The great variation in wild and cultivated native plums is possibly due to more or less remote hybridity.