PRIMROSE. The genus Primula contains numerous species distributed throughout the cooler parts of Europe and Asia, and found also on the mountains of Abyssinia and Java. They are all herbaceous perennials, possessing a permanent stock, from which are emitted tufts of leaves and flower-stems -which die down in winter; the new growths formed in autumn remain in a bud-like condition ready to develop themselves in spring. They form the typical genus of Primulaceae, the floral conformation of which is very interesting on several accounts independently of the beauty of the flowers. Thus the five stamens springing from the tube of the corolla, instead of being placed alternately with or between its lobes, are opposite or “super posed” to them, an arrangement accounted for by some on the supposition that an outer row of stamens (which, if present, would render the flower symmetrical) is suppressed. In support of this view the case of Samolus, an allied genus in which there are five petaloid stamens as well as five fertile ones, may be cited. By others the anomaly is explained on the hypothesis that the corolla is suppressed, what appears to be such being merely an outgrowth from the stamens. But this view is not borne out by observation of the development of the flower. Within the base of the corolla tube is the one-celled superior ovary, rising up into the centre of which is a dome-shaped placenta, quite detached from the walls of the ovary and studded with ovules. The origin and explanation of this free central placenta have formed the subject of a copious literature, the point at issue being whether the placenta is a direct prolongation from the axis of the plant or an outgrowth from the walls of the carpels. The variation in the length of the stamens and of the style in ...the flowers of this genus has attracted much attention since Darwin pointed out the true significance of these varied arrangements. Briefly it may be said that some of the flowers have short stamens and a long style, while others have long stamens, or stamens inserted so high up that the anthers protrude beyond the corolla tube, and a short style. Gardeners and florists had for centuries been familiar with these variations, calling the flowers from which the anthers protruded “thrumeyed” and those in which the stigma appeared in the mouth of the tube “pin-eyed.” Darwin showed by experiment and research that the most perfect degree of fertility, as shown by the greatest number of seeds and the healthiest seedlings, was attained when the pollen from a short-stamened flower was transferred to the stigma of a short-styled flower, or when the pollen from the long stamens was applied to the long style. As in any given flower the stamens are short (or low down in the flowertube) and the style long, or conversely, it follows that to ensure a high degree of fertility cross fertilization must occur, and this is effected by the transfer of the pollen from one flower to another by insects. Incomplete fertility arises when the stigma is impregnated by the pollen from the same flower. The size of the pollen-grains and the texture of the stigma are different in the two forms of flower. The discovery of the physiological significance of these variations in structure, which had long been noticed, was made by Darwin, and formed the first of a series of similar observations and experiments recorded from time to time in the Journal of the Linnean Society and elsewhere by himself and subsequent observers. Among British species may be mentioned the Common Primrose (Z j . vulgaris'); the Cowslip (P. veris), which is the original source of the Polyanthus of the gardens; the true Oxlip (P. elatior), a rare plant only found in the eastern counties; and the Common Oxlip, by some considered to be a form of the Common Primrose but provided with a stem supporting the flowers. Darwin’s experiments go to prove that the first-named three are species, while the last-named is a hybrid between the cowslip and the primrose. In addition to these species two others occur in Britain, namely, P. farinosa, found in Wales, the north of England, and southern Scotland, and P. scotica, which occurs in Orkney and Caithness. These two species are found also in high Arctic latitudes, and P farinosa, or a very closely allied form, exists in Fuego.
The Auricula of the gardens was formerly considered to be a form of P. Auricula, a yellow-flowered species, a native of the Swiss mountains, but it has been recently shown by Kerner that in all probability the origin of the Auricula was P. pubescens, supposed to be a natural hybrid between P, Auricula and P. hirsuta. The Polyanthus has already been mentioned as a variety of the cowslip, but it may further be added that some very remarkable forms which have been cultivated for centuries owe their peculiarities to the assumption by the ordinarily green calyx of a petaloid condition; when this is complete we have the Condition called “hose in hose” by the gardeners. This may, however, arise from actual duplication of the corolla λvithin the calyx. The Chinese Primrose, now so much cultivated in gardens, is derived from P. preenitens. The Japanese Primrose is nearly or quite hardy, and is the stateliest of the genus; its flowers of varied colours are placed tier above tier, like the branches of a fir tree. P. corl·usoides is another Japanese species of which many forms are now cultivated. P. simensis, with mealy leaves and yellow flowers, is the Abyssinian Primrose of gardens. The Himalayas are rich in species of primrose, often very difficult of determination or limitation, certain forms being peculiar to particular valleys. Of these P. denticulata, Stuartii, sikkim-mensis, nivalis, may be mentioned as frequently cultivated, as well as the lovely rose-coloured species P. rosea.
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