PRIMROSE. The genus Primula contains about 25o species distributed throughout the cooler parts of Europe and Asia, and found also on the mountains of Abyssinia and Java; a few are American. They are herbaceous perennials, with 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 in spring. They form the typical genus of Primulaceae (q.v.), the floral conforma tion of which is very interesting on several accounts independently of the beauty of the flowers.
The variation in the length of the stamens and of the style in the flowers of Primula has attracted much greater attention since Charles Darwin investigated them. 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 "thrum-eyed" and those in which the stigma appeared in the mouth of the tube "pin-eyed." Darwin showed by experiment that the most perfect degree of fertility, as shown by the greatest number of seeds and the health iest 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 flower-tube) and the style long, or conversely, it follows that to ensure a high degree of fertility cross fertilization must occur, and this is affected 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 differ ent in the two forms of flower.
Among British species may be mentioned the common primrose (P. vulgaris) ; the cowslip (P. veris) ; the true oxlip (P. elatior), a rare plant only found in the eastern counties ; and the common oxlip, the flowers of which recall those of the common primrose, but are provided with a supporting stem, as in the cowslip; it is, in fact, a hybrid between the cowslip and the primrose. In addition to these two other species occur in Britain, namely, P. farinosa, bird's eye primrose, found in Wales, the north of Eng land and southern Scotland, and P. scotica, which occurs in Ork ney and Caithness. These two species are found also in high Arc tic latitudes, and P. farinosa, or a very closely allied form, exists in Fuegia. About 15 species occur in North America, chiefly in the western and north-western parts of the continent.
The auricula (q.v.) of the gardens is derived from P. Auricula, a yellow-flowered species, a native of the Swiss mountains. The polyanthus (q.v.), a well-known garden race, is probably derived from a cross between the primrose and cowslip. The Himalayas are rich in species of primrose, often very difficult of determina tion or limitation, certain forms being peculiar to particular val leys. Of these P. denticulata, Stuartii, sikkimmensis, nivalis, floribunda, may be mentioned as frequently cultivated, as well as the lovely rose-coloured species P. rosea. The royal cowslip (P. imperialis) resembles P. japonica, but has leaves measuring 18 in. long by 5 in. wide. It grows at an elevation of 9,00o ft. in Java, and has deep yellow or orange flowers.
The primrose is to be had in cultivation in a considerable variety of shades of colour, ranging from the palest yellow to deep crimson and blue. As the varieties do not reproduce quite true from it is necessary to increase special kinds by division. The primrose is at its best in heavy soils in slight shade, and with plenty of moisture during the summer. One of the most popular of winter and early spring decorative plants is the Chinese prim rose, Primula sinensis, of which some superb strains have been obtained. P. japonica, a bold-growing and very beautiful Japa nese plant, is hardy in sheltered positions in England. P. cor tusoides, var. Sieboldii (Japan), of which there are many lovely forms, is suitable for outdoor culture and under glass. There are several small-growing hardy species which should be accommo dated on the best positions on rockeries where they are secure from excessive dampness during winter; excess of moisture at that season is the worst enemy of the choice Alpine varieties. They are propagated by seed and by division of the crowns after flowering. P. Forrestii is an orange-yellow flowered species from China; as is also P. Bulleyi. They are probably hardy—at least in favoured spots.
Evening primrose belongs to the genus Oenothera (family Onagraceae), natives of temperate North and South America. The common evening primrose, 0. biennis, has become naturalized in Great Britain and elsewhere in Europe ; the form or species known as var. grandiflora or 0. Lamarckiana is a very showy plant with larger flowers than in the common form. Other species known in gardens are 0. missouriensis (macrocarpa), 6 to 12 in., which has stout trailing branches, lance-shaped leaves and large yellow blossoms.
The name of Cape primrose has been given by some to the hy brid forms of Streptocarpus, a South African genus belonging to the family Gesneraceae.