Habit of growth, unlike size, varies but little with changing conditions and thus becomes a most important means of distinguishing species and varieties and not infrequently sets the seal and sign of desirability for an orchard cherry. More than any other character, habit of growth gives what is called "aspect" to a cherry tree. Thus, a species or a variety may be upright, spreading, round-topped, drooping or weeping in habit of growth; the head may be open or dense and may be formed by a central shaft with several whorls of branches or by three or four trunk-like stems each with its scaffolding branches. The trees may grow rapidly or slowly and may be long-lived or short-lived. The trunks may be short and stocky, or long and slender, straight or crooked, gnarled or smooth, these characters often determining whether a cherry is manageable or unmanageable in the orchard. The degree of hardiness is a very important diagnostic character for groups of cherries and often wholly indicates their value for agriculture. Thus, the varieties of _Prunus avium_ are but little hardier than the peach while those of _Prunus cerasus_ are as hardy or hardier than the apple. The range of varieties as to hardiness falls within that of the species and it is interesting to note that in Europe, where the wild _Prunus avium_ is very common, in the many centuries since the fruit has been under domestication, a cultivated variety hardier than the wild Sweet Cherry has not been developed. Cherries are designated in the technical descriptions as hardy, half-hardy and tender. Productiveness, age of bearing, and regularity of bearing are distinctive and valuable characters of orchard cherries but not of wild cherries. The care given the tree greatly influences fruitfulness, yet the quantity of fruit produced is often a helpful means of identifying a variety and is a character that must always be considered by the plant-breeder. Age of bearing and regularity of bearing are most important characters with the pome fruits, the apple, in particular, but while worth considering with the drupes are of relatively little value, all drupaceous fruits coming in bearing at about the same time for the species and all bearing regularly, as a rule, unless interfered with by some outside agency preventing the setting or causing the dropping of fruit.