The Pear (_Pyrus communis_) differs from the apple in the shape of the fruit (see _a_ in _fig_. 28), which tapers towards the footstalk, instead of being umbilicate, that is, indented at the point of the insertion of the footstalk, as is the case with the Apple. The construction of the flowers in both species is the same, except that the styles are quite free for their whole length in the Pear, and not partially united into a column as in the Apple. This distinction, and some others, have been thought, by some botanists, sufficient to constitute the Apple and its allied species into a separate genus under the name of _Malus_. The leaves of the Pear differ from those of the Apple in being the same colour on both surfaces, whereas those of the Apple are covered with a white down on the under side. Besides the Apple and the Pear, and their respective allies, which form two distinct sections of the genus Pyrus, that genus, being a very extensive one, is divided into several other sections, all the plants contained in which may be arranged under two heads: viz., those that formerly constituted the genus Sorbus; and those that were once called Aronia. [Illustration: FIG. 29.—FLOWER AND FRUIT OF THE MOUNTAIN ASH.] The Mountain Ash (_Pyrus aucuparia_) may be considered as a fair specimen of most of the trees belonging to the Sorbus division. By the details of the flowers of this species given in _fig._ 29, it will be seen that the petals (_a_) are very small and concave; and the calyx (_b_) is tubular, and five-cleft. There are three styles, as shown at _c_; and the stamens (_d_), which project far beyond the petals, are inserted in the disk. The fruit (_e_) is a pome with three seeds (_f_) enclosed in a cartilaginous membrane, like the core of the apple or pear. The leaves of the Mountain Ash are impari-pinnate, that is, they consist of several pairs of leaflets, terminating in an odd one; and the flowers are produced in corymbs. The White Beam-tree (_Pyrus Aria_), the wild Service (_P. torminalis_), and several similar trees, belong to this division and have the same kind of fruit as the Mountain Ash. The true Service, however, differs in its fruit being generally shaped like a pear, though there is a variety with apple-shaped fruit. One species (_P. pinnatifida_) has the leaves lobed to the midrib, instead of being cut into leaflets; and this gives the name to the species, leaves of this description being called pinnatifid. The leaves of the genus Pyrus often have their petioles dilated and somewhat stem-clasping at the base; but they have generally only small stipules. Among the other plants included in the genus Pyrus, may be mentioned the beautiful shrub now called _Pyrus arbutifolia_, which has been successively included in the genera Cratægus, Aronia, and Mespilus; and _P. Chamæmespilus_, which has been successively called Cratægus, Mespilus, and Sorbus. There are several beautiful low shrubs belonging to this division of the genus Pyrus.