480 



THE DICTIONARY OF GARDENING, 



Oidium continued. 



gunpowder strewn over the white or pale grey surface. 

 The perithecia usually bear, on their outer surface, simple 

 or forked hairs or prickles, the differences in which help 

 in distinguishing the species and genera of the group. 

 The number of asci in each perithecium, and the number 

 of spores in each ascus, differ considerably in the various 

 genera. There are many different kinds of Oidium, 

 but all have a characteristic appearance, that enables 

 an expert to recognise a member of the group, on seeing 

 the affected plant. Several of the species are met with 

 on uncultivated plants, others on cultivated ones; fre- 

 quently, they injure the latter very much, e.g., Erysiphe 

 graminis, on grass-leaves, as whitish spots on leaves and 

 stems of grasses; E. Martii, on Peas; and so forth. In 

 some species, e.g., E. graminis, the perithecia are formed 

 only under very favourable circumstances; hence they 

 are much better known as Oidium than in the perfect 

 state. This leads to a few species, the Oidium of which 

 is, at times, very plentiful and harmful, while their peri- 

 thecia remain unknown. In this latter group may be 

 noticed that found on Turnips, in various parts of Eng- 

 land, and also in Scotland, caused by an Oidium 

 (0. Balsamii) ; and the widely-known disease of the 

 Grape Vine, characterised by the formation of white 

 patches on leaves and Grapes, these patches belonging 

 to a Fungus only too famous as Oidium TucTceri. 



The various Oidia prove hurtful by absorbing the 

 protoplasm from the cells of their hosts, by means of 

 the small lobed branchlets pushed into the tissues of 

 the latter. The result of this is to cause the parts 

 attacked to become yellow and faded, and, after a time, 

 death of the part, or of the whole plant, ensues. The 

 Vines in many Vine-producing countries were exceed- 

 ingly injured by 0. Tuckeri; the Hops in England, and 

 elsewhere, are often seriously damaged by Sphasrotheca 

 Castagnei; and many other plants suffer, in greater or 

 less degree, from attacks of other species of this group. 



Remedy. The superficial position of the Fungi renders 

 direct treatment easy. A thorough application to the 

 diseased parts of the host-plants of flowers of sulphur, 

 or of potassium sulphide in weak solution, is found suffi- 

 cient to put an end to the growth of the Fungus, with- 

 out injuring the host. The solution has been recently 

 found most useful in the removal of Green Fly and Bed 

 Spider, as well as of Mildew. 



OIL NUT. A West Indian name for the seeds of 

 Ricinus communis. 



OIL PALM. See Elaeis. 



OLACINEJS!. An order of erect, climbing, or twin- 

 ing shrubs or trees, very rarely suffruticose or sub-herba- 

 ceous, dispersed over the tropical and sub-tropical regions 

 of the globe, a few growing in South Africa or extra- 

 tropical Australia. Flowers greenish, yellowish, or white, 

 rarely purplish, generally small ; calyx four or five (rarely 

 six) toothed, lobed, or parted ; petals four, five, or rarely 

 six, free, or coalescing in a campanulate or tubular corolla ; 

 inflorescence cymose, racemose, or paniculate. Fruit 

 usually drupaceous, one-seeded. Leaves alternate, or 

 rarely opposite, entire or occasionally toothed, often 

 penninerved ; petioles usually flexuous ; stipules none. 

 The order includes thirty- six genera and about 170 

 species. Examples : Heisteria, Icacina, and Olax. 



OLAX (from olax, a furrow ; flowers partially fur- 

 rowed or imbricated). STNS. Fissilia, Lopadocalyx, 

 Spermaxyrum. OBD. Olacinece. A genus of about 

 twenty-two species of stove, often climbing, glabrous 

 trees, shrubs, or sub-shrubs ; eight are found in Aus- 

 tralia, ten in tropical Asia, and four are indigenous to 

 tropical Africa or Madagascar. Flowers small, disposed 

 in short axillary spikes or racemes, rarely solitary. Leaves 

 alternate, often distichous, entire, articulated with the 

 branches. The undermentioned species, probably the only 



Olaz continued. 



ones known to cultivation, thrive in a compost of sandy 

 peat, fibry loam, and a little dried leaf mould. Propa- 

 gated by cuttings of ripened shoots, inserted in sand, 

 under a bell glass, in heat. 



O. imbricata (imbricated). /. white ; racemes axillary, imbri- 

 cated. December, fr. ovate. I. oblong, or oblong-lanceolate, 

 bifarious, entire, shining. East Indies, 1820. Climbing shrub. 



O. scandens (climbing). /. white, racemose; petals six. 

 December. I. pubescent beneath. Stem prickly ; branches 

 terete, climbing. Coromamlel, 1820. Shrub. 



O. Stlicta (upright), fl. white, abortive. I. oblong-linear, 

 mucronate. Australia, 1820. Erect glabrous shrub. SYN. Sper- 

 maxyrum strictum. 



OLDENLANDIA (named after Henry Bernh. 

 Oldenland, a Dane, who collected plants at the Cape 

 of Good Hope). OBD. Rubiaceee. An extensive genus 

 (about seventy species) of stove or greenhouse, slender, 

 erect or diffuse herbs, sometimes shrubby at base; they 

 abound in tropical and sub-tropical regions, being 

 mostly found in Asia. Flowers white or pink, small, in 

 axillary or terminal panicles, or rarely solitary. Leaves 

 opposite, narrow, frequently small. The species have no 

 horticultural interest. 



OLDFIELDIA (named after E. A. Oldfield, a mer- 

 chant at Sierra Leone). OED. Euplwrbiacece. A mono- 

 typio genus, the species being a stove evergreen tree. 

 It thrives in a mixture of loam, leaf mould, and sand, 

 and requires an abundance of water when in rapid growth. 

 Propagated by cuttings. 



O. africana (African), fl., males loosely cymulo.se, the small 

 cymes axillary, on peduncles shorter than the petioles ; female 

 flowers unknown. I. opposite, long-stalked, digitately five to 

 seven-foliolate ; leaflets petiolulate, entire, coriaceous, penni- 

 veined. Tropical Western Africa. The timber of this tree is 

 believed to be the African oak or teak. 



OLD MAN. A common name applied to Artemisia 

 Abrotanum and Rosmarimts ojficinalis. 



OLD MAN'S BEARD. See Clematis Vitalba 

 and Saxifraga sarmentosa. 



OLEA (the old Latin name, akin to the Greek Elaia, 

 the Olive). Olive. ORD. Oleaceaz. A rather large genus 

 (about thirty-five species) of usually greenhouse ever- 

 green trees, natives of tropical and central Asia, the 

 Mediterranean region, tropical and South Africa, the 

 Mascarene Islands, and New Zealand. Flowers white, in 

 axillary and terminal panicles, small ; corolla funnel- 

 shaped, with a short tube ; inflorescence mostly or almost 

 totally centripetal. Drupe ovoid, oblong, or globose. 

 Leaves opposite, entire or rarely toothed. The species 

 here described are those best known to cultivation. 

 Oleas thrive in well-drained loam, and are of the easiest 

 cultivation. They are propagated by cuttings of the 

 ripened young shoots, or by seeds. 



O. capensis (Cape), fl. disposed in racemose terminal panicles, 

 June. fr. rather wrinkleil, size of a pea. I. oblong, coriaceous, 

 dense and rigid, decussate, always paler beneath. Branches 

 rather tetragonal, from decurrent lines. A. 5ft. Cape of Good 

 Hope, 1730. (B. R. 613.) 



O. europeea (European). Wild Olive, fl. panicled. June to 

 August, fr. small, of no value. I. oblong, mucronate, quite 

 entire, shorter and stiffer than those of the cultivated Olive, 

 hoary beneath while young. Branches rather quadrangular, 

 hoary. South Europe, &c., 1821. This small tree is nearly hardy. 

 SYN. 0. Oleaster. 



O. e. sativa (cultivated), fl. small, panicled. August. I. lanceo- 

 late, mucronate, quite hoary beneath. Branches angular, but 

 not spinescent. South Europe, 1570. SYN. 0. sativa. 



O. fragrans (fragrant). A synonym of Osmanthus fragrans. 



O. iliclfolia (Holly-leaved). A synonym of Osmanthus Aqui- 

 folium. 



O. laurifolia (Laurel-leaved). fl. disposed in terminal, loosely 

 trichotomous panicles. Summer, fr. sub-globose. I. oblong, 

 acuminate at both ends, more or less undulated, or flat, entire, 

 glabrous, petiolate ; petioles Jin. long. Cape of Good Hope. 

 (B. M. 3089 and L. B. C. 379, under name of 0. undulata.) 



O. Oleaster (Oleaster). A synonym of 0. europcca. 



O. sativa (cultivated). A synonym of 0. europcea sativa. 



O. undulata (wavy). A synonym of O. laurij'ulia. 



