Soon after the appearance of the Dog Violet--usually early in May--we meet with the flowers of the Wood Sorrel or Alleluia (_Oxalis Acetosella_), a plant which is often included with the Crane's-bills in the order _Geraniaceæ_, but sometimes placed in a separate small order (_Oxalidaceæ_) containing only three British species. It is a very pretty little plant, of an acid nature, springing from a creeping rhizome. The leaves are radical, ternate, hairy, and sensitive, folding vertically at night in such a manner that the lower surfaces, containing the stomata, are completely covered, and thus loss by evaporation prevented. The flowers are usually solitary and axillary, and the peduncle has two small bracts about half way up. There are five sepals, united below; five white or pinkish petals; and ten stamens, all united into one bundle, but five shorter than the others. The ovary is five-chambered, and the fruit is a capsule. Like the Violet, this flower is particularly interesting both as to the nature of its flowers, and to the manner in which it scatters its seeds. It bears two kinds of flowers--the delicate spring flowers just described, which are barren; and the later inconspicuous blooms, without petals, and which do not open, but produce seeds. The latter kind of flower may be seen up to August and September. [Illustration: THE WOOD SORREL.] When the ovary is ripe it splits longitudinally along five seams, but the seeds remain attached to the placenta. Now, the seed coat is made up of layers, one of the inner of which becomes highly strained as the ripening proceeds, while the outer coat is not so strained. When the seed is quite ripe the cell-walls of the deeper layer swell, thus exerting a pressure on the outer layer, which is at last rent. The edges of the slit formed suddenly roll back, and the seed is violently jerked out through the opening of the capsule immediately in front of it. In April, and from this month to about the end of July, the Wood Strawberry (_Fragaria vesca_--order _Rosaceæ_) is in flower. There is no mistaking this species when in fruit, but at other times the Barren Strawberry (_Potentilla Fragariastrum_), also called the Strawberry-leaved Cinquefoil, is often confused with it. The latter may be known by the absence of runners. The chief distinguishing features of the Wood Strawberry are the running stem; ternate leaves, with sessile, hairy, serrate leaflets; hairy, erect peduncles; and white flowers, about half an inch in diameter, on pedicels which droop when in fruit. In shady woods grows the Sweet Woodruff (_Asperula odorata_--order _Rubiaceæ_)--a small, erect and smooth plant, seldom exceeding eight inches in height. The leaves are six to nine in each whorl, lanceolate, with small prickles on the margins. The flowers are white, in terminal panicles, and the fruit is rough with hooked hairs. The herb emits, when dry, a pleasant odour resembling that of new hay. [Illustration: THE SWEET WOODRUFF.]