In variability the Insititia plums are quite the reverse of the Domesticas, almost wholly lacking this quality. These plums have been cultivated over two thousand years, yet there is seemingly little difference between the sorts described by the Greeks and Romans at the beginning of the Christian Era and those we are now growing. So, too, one often finds half-wild chance seedlings with fruit indistinguishable from varieties under the highest cultivation. This pronounced immutability of the species is one of its chief characteristics. There are probably several sub-divisions of _Prunus insititia_ but material does not exist in America for the proper determination of the true place for these forms, and the Old World botanists cannot agree in regard to them. It is probable that _Prunus subsylvestris_ Boutigny[61] and _Prunus pomarium_ Boutigny[62] belong to _Prunus insititia_ and almost beyond question _Prunus syriaca_ Koehne[63] is the yellow-fruited Mirabelle of this species. _Prunus insititia glaberrima_ Wirtg,[64] occasionally found in the herbaria of Europe has, with its small, roundish-obovate leaves, but little appearance of _Prunus insititia_ and may be, as Schneider surmises,[65] a cross between _Prunus spinosa_ and the Myrobalan of _Prunus cerasifera_. The Insititia plums are second in importance only to the Domesticas. Their recorded history is older. This is the plum of the Greek poets, Archilochus and Hippona, in the Sixth Century B. C.[66] Theophrastus, the philosopher, mentioned it three hundred years before Christ, as did Pollux, the writer and grammarian, a century before the Savior, while Dioscorides, the founder of botany, during the last named period, distinguishes between this plum and one from Syria, presumably a Domestica. This is one of the twelve kinds of plums described by Pliny (see page 17) who calls it the Damascene, so-called from Damascus in Syria, and says of it, “introduced long since into Italy.” It is the Damask plum of Columella when in his tenth book he says: “then are the wicker baskets cramm’d With Damask and Armenian and Wax plums.” The yellow plums of the Roman poets, Ovid and Vergil, are probably the Bullaces or Mirabelles of this species. Indeed, its cultivation was probably prehistoric, for Heer[67] has illustrated and described stones of a plum found in the lake-dwellings of Robenhausen which can be no other than those of Insititia. The authentic written history of this plum may be said to have begun with or a little before the Christian Era. The records of the cultivation and development through the early centuries of the present chronology and the Middle Ages to our own day may be found in the herbals, botanies, pomologies, agricultural and general literature of the past two thousand years.