PRIMROSE. 1 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; 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 remains in a bud-like condition ready to develop in spring. They form the typical genus of Primulaceae (q.v.), the floral conformation 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 attention since Charles 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 " 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 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 flower-tube) and the style long, or conversely, it follows that to ensure a high degree of fertility cross fertih'zation 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 (see figure under PRIMULACEAE). 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 by himself and subsequent observers (see Darwin, Different Forms of Flowers, etc.). 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 1 Lat. primula; Ital. and Span, primavera; Fr. primevere, or in some provinces primerole. Strangely enough, the word was applied, according to Dr Prior, in the middle ages to the daisy (Bellis perennis), the present usage being of comparatively recent origin.
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, 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 Fuegia.
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 determination or limitation, certain forms being peculiar to particular valleys. Of these P. denliculata, Stuartii, sikkimmensis, nivalis, floribunda, may be mentioned as frequently cultivated, as well as the lovely rose-coloured species P. rosea.
The Royal Cowslip (P. imperialist resembles P. japonica, but has leaves measuring 18 in. long by 5 in. wide. It grows at an elevation of 9000 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 seed, 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 primrose, Primula sinensis, of which some superb strains have been obtained. For ordinary purposes young plants are raised annually from seeds, sown about the beginning of March, and again for succession in April and, if needed, in May. The seed should be sown in well-drained pots or pans, in a compost of three parts light loam, one part well-rotted leaf-mould, and one part clean gritty sand, as it does not germinate freely if the soil contains stagnant moisture, afterwards placing a sheet of glass over the pans to prevent evaporation of moisture. When the seeds germinate, remove the glass and place the pans in a welllighted position near the glass, shading them from the Sun with thin white paper, and giving water moderately as required. When the seedlings are large enough to handle, prick them out in pans or shallow boxes, and, as soon as they have made leaves an inch long, pot them singly in 3-in. pots, using in the soil a little rotten dung. They should then be placed in a light frame near the glass in an open situation, facing the north. When their pots are filled with roots they should be moved into 6-in. or 7-in. pots. The soil should now consist of three parts good loam broken with the hand, one part rotten dung and leaf-mould, and as much sand as will keep the whole open. They should be potted firmly, and kept in frames close up to the glass till September, excess in watering being carefully avoided. In the autumn they should be transferred to a light house and placed near the glass, the atmosphere being kept dry by the occasional use of fire-heat. The night temperature should be kept about 45. When the flowering stems are growing up, manure water once or twice a week will be beneficial. The semi-double varieties are increased from seeds, but the fullydouble ones, and any particular sort, can only be increased by cuttings. Primula japonica, a bold-growing and very beautiful Japanese plant, is hardy in sheltered positions in England. P. cortusoides, 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 accommodated 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 a quite new 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 (natural order Onagraceae), natives of temperate North and South America. The common evening primrose, Oe. biennis, has become naturalized in Britain and elsewhere in Europe; the form or species known as var. grandiflora or Oe, Lamarckiana is a very showy plant with larger flowers than in the common form. Other species known in gardens are Oe. missouriensis (macrocarpa) , 6 to 12 in., which has stout trailing branches, lance-shaped leaves and large yellow blossoms; Oe. taraxacifolia, 6 to 12 in., which has a stout crown from which the trailing branches spring out, and these bear yery large white flowers changing to delicate rose; this perishes in cold soils, and should therefore be raised from seed annually. Of erect habit are Oe. speciosa, I to 2 ft., with large white flowers; Oe. fruticosa, 2 to 3 ft., with abundant yellow flowers.
The name of Cape Primrose has been given by some to the hybrid forms of Streptocarpus, a South African genus belonging to the natural order Gesneraceae.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)