ONONIS ARVENSIS.—­Restharrow.  A native undershrub of very variable size, according to the position in which it is found growing.  It creeps along the ground, the shoots sending out roots as they proceed, and is usually found on dry sandy banks.  The flowers when at their best are very ornamental, being bright pink, and with the standard streaked with a deeper shade.  They are abundantly produced, and render the plant very conspicuous during the summer and autumn months.  When planted on an old wall, and allowed to roam at will, the Restharrow is, perhaps, seen to best advantage.

OSMANTHUS.

OSMANTHUS AQUIFOLIUM ILLICIFOLIUS.—­Holly-leaved Osmanthus.  Japan.  This is a handsome evergreen shrub, with Holly-like leaves, and not very conspicuous greenish-white flowers.  It is a very desirable shrub, of which there are varieties named O.A. ilicifolius argenteo-variegatus, O.A. ilicifolius aureo-variegatus, and O.A. ilicifolius nanus, the names of which will be sufficient to define their characters.

O.A.  ILICIFOLIUS MYRTIFOLIUS.—­Myrtle-leaved Osmanthus.  A very distinct and beautiful shrub, with unarmed leaves.  It is of dwarf, compact growth, with small, sharply-pointed leaves, and inconspicuous flowers.  For the front line of a shrubbery this is an invaluable shrub, its pretty leaves and neat twiggy habit making it a favourite with planters.  The variety rotundifolius is seldom seen in cultivation, but being distinct in foliage from any of the others is to be recommended.  They grow freely in any good garden soil, but all the better if a little peat is added at the time of planting.

OSTRYA.

OSTRYA CARPINIFOLIA (syn O. vulgaris).—­Common Hop Hornbeam.  South Europe, 1724.  A much-branched, round-headed tree, with cordate-ovate, acuminate leaves.  Both this and the following species, by reason of the resemblance between their female catkins and those of the Hop, and between their leaves and those of the Hornbeam, have acquired the very descriptive name of Hop Hornbeam.  This is a large-growing tree, specimens in various parts of the country ranging in height from 50 feet to 60 feet.

O. VIRGINICA.—­Virginian Hop Hornbeam.  Eastern United States, 1692.  Resembles the latter, but is of smaller growth, rarely exceeding 40 feet in height.  They grow fairly well in almost any class of soil, and on account of the long and showy catkins are well worthy of cultivation.

OXYDENDRUM.

OXYDENDRUM ARBOREUM (syn Andromeda arborea).—­Sorrel-tree.  Eastern United States, 1752.  Unfortunately this species is not often found under cultivation, being unsuitable generally for our climate.  In some instances, however, it has done well, a specimen in the Knap Hill Nursery, Surrey, being 30 feet high, and with a dense rounded head.  The flowers are very beautiful, being of a waxy white, and produced abundantly.  It wants a free rich soil, and not too exposed site.