Our first species is the well-known Wallflower (_Cheiranthus cheiri_), of the order _Cruciferæ_. It is a rather shrubby plant, frequent on old walls and ruins, where it flowers during April and May. Though too familiar to need any description, we may note that in the wild state it varies from six to twelve inches high, and bears sweetly-scented, yellow or orange flowers. The plant is not indigenous, but has now become naturalised as a wild flower in most parts of Britain. The Wall Rocket (_Diplotaxis tenuifolia_ or _Brassica tenuifolia_), of the same order, is a very similar plant, growing in similar situations, but it does not commence to flower till the summer is somewhat advanced. Its stem is leafy, branched, smooth, woody towards the base, but more slender than that of the Wallflower; and its very variable leaves are generally three or four inches long, deeply divided pinnately into narrow segments with irregularly-toothed margins, and emit a rather unpleasant odour when rubbed. The flowers are of a pale yellow colour, fragrant, about three-quarters of an inch in diameter, in terminal racemes, with sepals more or less spreading; and the fruits are narrow, flattened siliquas, with membranous valves, about an inch and a half long. The plant is to be found principally in the southern counties of England, and flowers from July to September or early October. On dry rocks, chiefly in the hilly and mountainous districts of North and West Britain, we meet with the Vernal Sandwort (_Arenaria verna_) of the order _Caryophyllaceæ_. This is a little tufted plant, only from two to four inches high, with branched stems more or less decumbent at the base; and small, sessile, opposite, very narrow leaves, each with three veins. The starlike, white flowers are about a third of an inch across, on slender stalks, and grouped in terminal, loose, few-flowered cymes. They have five pointed sepals, less than a quarter of an inch long, each with three prominent veins; five spreading petals, a little longer than the sepals; ten stamens; and a superior ovary with three narrow styles. The fruit is a short ovate capsule which opens, when ripe, by three valves. One of the Geraniums--the Shining Crane's-bill (_Geranium lucidum_)--is almost essentially a plant of walls and rocks. It is a beautiful species, smooth and shining in all its parts, with a tendency to turn red, like the Herb Robert; and, as in other plants of its order (_Geraniaceæ_), distinguished by the swollen joints of its stem. The leaves are almost round in general outline, but are deeply divided into five, broad, coarsely-toothed segments. The flowers are small, rose-coloured, and generally grow in pairs on axillary stalks. They have five, erect, wrinkled sepals, with long points; and five short, rather broad, entire petals. This species is common in most parts of Britain. It varies in height from six to eighteen inches, and flowers from May to September.