This section is from the book "Wayside And Woodland Blossoms", by Edward Step. Also available from Amazon: Wayside And Woodland Blossoms: A Guide To British Wild-Flowers.
Viola odorata. - Violaceae. There is one other native species :The Pasque-flower (A. Pulsatilla). Blossoms before the leaves mature. Flowers dull purple; exterior covered with silky hairs; leaves also silky. Fruit, little nutlets (achenes) provided with long feathered awns, with which they float on the wind when ripe. Flowers, May and June, on chalk downs and limestone pastures in Essex and Gloucestershire, and from York to Norfolk.
One of the most valued flowers of spring in cities is the cultivated violet, and the rambler from town considers himself fortunate if he comes upon a sheltered bank whereon the wild Sweet Violets grow. We need not dwell at any length upon the special characters of this species, for its possession of sweet perfume is sufficient alone to separate it from the related species comprised in the genus Viola.
It will be seen to have a short rootstock, and to give off runners. The leaves are broadly heart-shaped, and have a way of enlarging after the plant has flowered - a characteristic shared by the Marsh Violet and the Hairy Violet. The flowers vary in colour ; they may be blue, reddish-purple, or white. The petals are unequal in size and shape, there being two pairs and an odd one. This is larger than the others, and is produced backwards as a short hollow spur. It is really the uppermost of the five petals, but, owing to the flower-stalk (peduncle) invariably bending over near the summit, it appears to us always as the lowest.
A careful examination of the form and mechanism of the essential organs of this genus will be well repaid by the light thrown upon Nature's methods to secure the continuity of species. The style on arising from the ovary is thin and bent, but gradually expands until the stigmatic surface is very broad in comparison. The stamens surround the style, the anthers so closely touching each other laterally that they enclose a space in which the ovary and style occupy the centre, and from which the stigma protrudes. The anthers shed their pollen, which is dry, into this space. Two of the stamens send out each a long tail into the hollow petal-spur, which secretes honey from its tip. The reason why the flower-stalk bends over is, that the stigma may hang down instead of being erect. A bee smells the honey and alights on the odd petal. The dark lines converging to the spur show where the honey lies, but the thickheaded stigma blocks the way. Thrusting in his tongue, the bee pushes the stigma aside with his head, which is the more easily accomplished owing to the thin base of the style. But this act also disarranges the anthers, and as a result the loose pollen drops out upon his hairy head, where it will come in contact with the viscid stigma of the next violet he visits. In this way an occasional cross is effected that the vigour of the race may be maintained, but for ordinary purposes of reproduction the violet has a more economical method. When the spring season is over the violet ceases to furnish flowers got up for show, and sets about producing buds which will never open (cleistogamous). These are without petals, and contain nothing but the essential organs ; the anthers produce only enough pollen to fertilize the ovules in the ovary, which then develop into perfect seeds.
Viola odorata is found truly wild only in the S. and E. of England, and possibly the E. of Ireland; but it is naturalized in many other parts of the kingdom. Flowers, March to May. The name Viola is Latin, and is that by which the ancients knew it. There are six other British species, which will be found enumerated on page 58.