Pai 
* 
{ 
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 ip. 
The number of asci in each perithecium, 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 Oidiwm than in the perfect 
state. This leads to a few species, the Oidiwm 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 
(O. 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 Oidiwm Tuckeri. 
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 O. Tuckeri; the Hops in England, and 
elsewhere, are often seriously damaged by Spherotheca 
Castagnet; 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 Red 
Spider, as well as of Mildew. 
OIL NUT. A West Indian name for the seeds of 
Ricinus communis. 
OIL PALM. See Elaëis. 
OLACINEZ:. 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 Sonth 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 Olas. 
OLAX (from olaz, a furrow; flowers partially fur- 
rowed or imbricated). Syns. Fissilia, Lopadocalyz, 
Spermaxyrum. ORD. Olacineæ. 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 
Olax—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). jl. white; racemes axillary, imbri- — 
cated. December. jr. ovate. l. oblong, or oblong-lanceolate, 
bifarious, entire, shining. East Indies, 1820. Climbing shrub. — 
O. scandens (climbing). fl. white, racemose; petals six. 1 
December. l. pubescent beneath. Stem prickly; branches 
terete, climbing. Coromandel, 1820. Shrub. 
O. stricta (upright). fl. white, abortive. 
maayrum strictum. é 
OLDENLANDIA (named after Henry Bernh. 
Oldenland, a Dane, who collected plants at the Cape 
of Good Hope). ORD. Rubiacew. 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 R. A. Oldfield, a mer- 
chant at Sierra Leone). ORD. Ewphorbiacee. A mono- 
n tree. 
It thrives in a mixture of loam, leaf mould, and sand, 
and requires an abundance of water when in rapid 
typic genus, the species being a stove eve 
growth. Propagated by cuttings. 
O. africana (African). fl., males loosely cymulose, the small 
cymes axillary, on peduncles shorter than the petioles; female 
flowers unknown. J, 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 Rosmarinus. officinalis. 
OLD MAN’S BEARD. See Clematis Vitalba. 
OLEA (the old Latin name, akin to the Greek Elaia, — 
the Olive). Olive. ORD. Oleaceæ. 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. 
here described are those best known to cultivation. 
Oleas thrive in well-drained loam, and are of the easiest 
cultivation. 
ripened young shoots, or by seeds. 
O. capensis 2. jl. disposed in racemose terminal panicles, 
er wrinkled, size of a pea. J. oblong, coriaceous, — 
June. fr. rat 
dense and rigid, decussate, always paler beneath. Branches 
rather tetragonal, from decurrent lines. h. 5ft. Cape of Good A 
Hope, 1730. (B. R. 613.) 
O. europæa (European). Wild Olive. fl. panicled. June to 
August. Jr. small, of no value. Z. oblong, mucronate, quite 
entire, shorter and stiffer than those of the cultivated Olive, 
hoary beneath while young. Branches rather quadrangular, — 
hoary. South Europe, Åc., 1821. This small tree is nearly hardy. 
Syn. O. Oleaster. 
O. e. sativa (cultivated). f. small, panicled. August. J, lanceo- 
late, mucronate, quite hoary beneath. Branches angular, but 
not spinescent. South Europe, 1570. Syn. O. sativa. E 
O. fragrans (fragrant). A synonym of Osmanthus fragrans. 
Veet (Holly-leaved). A synonym of Osmanthus Aqui- 
ium, 
O. laurifolia (Laurel-leaved), H. disposed in terminal, loosely 
trichotomous panicles. 8 fr. sub-globose. 
acuminate at both ends, more or less undulated, or 
glabrous, petiolate; petioles zin. long. Cape of G 
(B. M. 3089 and L. B. C. 379, under name of O. undulata.) 
O. Oleaster (Oleaster). A synonym of O. europea. 
O. sativa (cultivated). A synonym of O. europea sativa. 
O. undulata (wavy), A synonym of O. laurifolia. 
The species 
They are propagated by cuttings of the 
Laue 
l. oblong-linear, 
mucronate. Australia, 1820. Erect glabrous shrub. SYN. Sper- — 
