From the western portion of the Old World, including all of Europe, northern Africa, Asia Minor, Persia, Turkestan and Afghanistan come 14 species. From this region, though the number of species as compared with East Asia is small, we have all of the cultivated esculent cherries, if possibly _Prunus tomentosa_ be excepted. Though nearly all of the species of this large territory are found--possibly all originated there--in the southeastern part of Europe and the adjoining southwestern part of Asia, yet they seem, with one or two exceptions, to be quite distinct from the species of the eastern half of the Old World--the Himalaya Mountains separating the two regions. It is probable that when west central Asia has been as well explored botanically as the east central part of the continent, many new species will be added to Prunus and its sub-genus Cerasus.
It is in the eastern half of the Old World that the cherry flora is richest. More than 100 of the 119 species of Cerasus recognized by Koehne are found in the Himalaya Mountains and the region to the east including Japan and the Kuril Islands. Yet out of all of this wealth of raw material only _Prunus tomentosa_ has been truly domesticated as an esculent though possibly a score of these species are well-known ornamentals. Of the 100 eastern Asiatic species about 75 belong to China--the remainder to Formosa, Siam and Japan with its islands. Happily these Chinese cherries are being introduced, but a few at a time, it is true, to Europe and America and it can hardly be otherwise than that they will enrich horticulture as they are domesticated, hybridized or used as a consort upon which to grow the cherries now known to cultivation. In particular, it may be expected that cherries for the cold north and the bleak plains of our continent will be evolved from the Asiatic species better suited to these regions than the cultivated cherries we now grow.
The number and diversity of the species of cherries which this brief review of Cerasus shows to exist suggest that our cultivated cherry flora is but begun. There can be no question but that others of these species than the few that have been domesticated will yield to improvement under cultivation and furnish refreshing fruits. It is just as certain that new types, as valuable perhaps as the hybrid Dukes we now have, can be produced through hybridization. In North America, we have no satisfactory stock for cultivated Sweet and Sour Cherries. Both of the stocks now commonly used, the Mazzard and the Mahaleb, as we shall see, have weaknesses that unfit them for general use. Surely out of the great number of forms we have just listed a better stock than either of the two named can be found. No doubt, too, many of these new species, even though they do not furnish food, will prove valuable timber or ornamental trees.