OIDIUM. 



OLD RED-SANDSTONE. 





OIDIUM, a genus of Plants belonging to the order of Fungi, some 

 of the species of which are found upou the human body and others 

 attack plants. It is known by possessing a simple or branched 

 mycelium, which is very minute and pellucid, aggregated into floccu- 

 lent masses slightly interwoven and articulated. The sporidia are 

 simple and pellucid, and arise from the joint of the mycelium. 



0. aOncara, the Thrush-Fungus, is found in the mucous membrane 

 of the mouth, fauces, and oesophagus of sucking children, and also 

 occasionally in grown-up persons in a state of extreme exhaustion. 

 The ulcerations, amidst the discharge of which this fungus is found, 

 are usually called thrush. Although constantly present in this disease 

 the fungus does not appear to produce the disease but to be the result 

 of the changes produced in the mucous membrane. It has been 

 observed that the mucous membrane in this state constantly affords 

 an acid reaction, and this acidity seems necessary to the growth of 

 the fungus. The best account of this fungus will be found in Robin's 



Hiatoire des Vege'taux Parasites.' Several other species of Oidlum 

 have been described. The fungus found in connection with the 

 recent grape-vine disease is an Oidium. [EuTOPnYTA ; FUNGI.] 



OIL-PALM. [EiJEis.1 

 OIL-TREE. [BASSIA.] 



OILS are substances of organic origin, and are found in both the 

 animal and vegetable kingdoms. They are divided into Fixed and 

 Volatile. The latter are principally products of the vegetable king- 

 dom. The Fixed Oils are composed of carbon, hydrogen, and oxygen. 

 Their general formula is C,,, H 10> 0. They are liquid or solid 

 according to the manner in which their element* are disposed. Most 

 of them are composed of two compounds, a liquid called Olein, and a 

 solid called Margariu, or another called Stearin. According as these 

 solid substances abound in oils, they are liquid or solid at the ordinary 

 temperatures of our atmosphere. Fixed Oil is found iu the fat or 

 adipose tissue of animals. [ADIPOSE TISSOE ; FAT.] 



Fixed Oil is found amongst plants principally in their seeds. In 

 gome cases as in the Olive [OLEA] it is yielded by the fruit. 



Some families of plants especially abound in oil. Thus among 

 the (Jrucifera we have Mustard, Rape, and Colza seed oil, with 

 other species cultivated in Europe, India, and Japan, of which some 

 have of late years been imported into this country. Several of 

 the family of Composite secrete oil in quantities large enough to 

 render it desirable to cultivate them for this purpose alone, as the 

 sunflower and Jerusalem artichoke, also some species of Carthamui, 

 or Bastard Saffron, and also the VerbetVM tativa of India, now known 

 to be identical with the Abyssinian Guizotia oleifcra, and of which 

 the oil is known in commerce by the name of Hutsyellow oil. So 

 Madia tativa yields Madi oil, and its seeds are said to be more 

 abundant in oil than any plant introduced into Europe. Most of the 

 Cucurbitacm also, aa the Melon, Qourd, Cucumber, and tfie numerous 

 varieties, cultivated especially in India, contain a large proportion of 

 oil, which is expressed in the East, as it formerly was in Europe. 

 The Roiacea; also store up a large proportion of oil in the kernels of 

 their fruit, as in the Almond, which is particularly valued ; so also 

 that of the Apricot, as well as that of the lirianc;on Apricot, and other 

 species of I'rmitu. In the Himalayas, oil is also expressed from the 

 Apricot kernel, and has been sent to this country of a fine quality. 



Among tbu Amentacea we have also several species which yield oil 

 of good quality, and in sufficient quantity to repay the expense of 

 expression, as Nut oil, obtained from the Hazel ; Beech-Nut oil, from 

 Fayus lyhatica ; with these may be mentioned Walnut oil, from 

 Juylan* n'yia. Besides these, Poppy oil, Ben-Nut oil (Jlt/peranthera), 

 Ground-Nut oil (A rachil), Physic-Nut oil (Jalropha), are well known. 

 So the cotton-seed yields oil, which is also the case with the seeds ol 

 the tea-plant, especially of the species called Thra old/era, and some 

 of the Camellias. 



Two species of Battia, B. longifolia and B. laiifolia, both yield oil 

 another species, B. butyracea, yields a vegetable butter, and is com 

 monly known as the Ghee, or Butter-Tree of Almora, [BASSIA]. The 

 native name of this tree is Choonee, and Mr. Traill describes it as not 

 being found in Kemaon, but in the adjoining Goorkhal province o: 

 Dotee. [Cocos; CKOTON; MYRISTICA; THKOBROMA; OLEA; PAPAVER; 

 BRASSIOA; EL^IS; RICINCS; AMIUDALUS.] 



The volatile oils are very numerous in the vegetable kingdom 

 They are called volatile on account of the ready manner in which they 

 may be volatilised under the influence of heat. The facility with 

 which they are diffused in the atmosphere renders them easy o 

 detection, and it is to this class of substances that plants owe their 

 peculiar odour?. Many of them are employed in perfumery, others 

 are used as stimulants in medicine, and some are poisons. Their 

 composition is much more varied than that of the fixed oils, and to 

 hemist they offer an exceedingly interesting field of research 

 Many of them have a constitution analogous to the compounds 

 obtained by chemists from the compound radicals. [COMPOUND 

 RAUICAU, in AIITS AND Sc. Div.] They are divided by chemists into 

 three groups : 1, those containing only carbon and hydrogen, as oil 

 of turpentine ; 2, those containing also oxygen, as oil of cloves ; 3, 

 those containing sulphur, as oil of garlic. Many natural orders are 

 characterised by yielding volatile oils. Thus the Lamiacete, Mi/rtaceas, 

 and others, embrace species all of which contain volatile oil in their 

 leaves. Mnny of the UmMlifcrrt yield a volatile oil in their fruit*. 



The petals are often the seat of these secretions, and especially those 

 most prized as the Rose, the Jasmine, the Heliotrope, and many others. 

 OKENITE is a Mineral, a variety of Dysclasite. It occurs in 



ibrous masses, having a radiated structure ; also imperfectly fibrous, 

 or composed of minute crystals. Its hardness is 4'5 to 5. Colour 

 white. Specific gravity 2'28. It exhibits double refraction. It is 

 ? ound at Disco Island, Greenland. Its analysis b.y Kobell afforded 



Silica 56-99 



Lime 26'35 



Water . 16-65 



-99-99 



OLACA'CE-iE, a small natural order of Exogenous Plants, chiefly 

 'ound within the tropics. Its most important characters are a small 

 inferior calyx, often becoming enlarged around the ripe fruit, a poly- 

 setalous valvate corolla, a small number of hypogynous stamens, partly 

 fertile and partly barren ; a 1-celled ovary, with pendulous ovules, 

 indehiscent fruit, and a small embryo amongst a large quantity of 

 albumen. Its affinities are little understood, but are supposed to be 

 jreatest with Pittosporacew, on the one hand, and Aurantiaccce, on the 

 other. The plants are of little importance for useful qualities ; one 

 species, Heitteria coccinca, is erroneously supposed to yield the Partridge- 

 Wood of cabinet-makers. The fruit of some species is eatable when 

 ripe, though not very pleasant. There are 21 genera and 48 species 

 in this order. 



OLD RED-SANDSTONE. By this title English geologists have 

 almost universally designated the variable series of rocks which 

 separate the youngest slates (Transition Rocks) from the mountain- 

 limestone and coal. Messrs. Conybeare and Phillips (' Geology of 

 England and Wales ') ranked the Old Red-Sandstone in their Medial 

 Order along with the coal and mountain-limestone; and this classifi- 

 cation has been unreservedly followed till within a short period. 

 Sir Roderick Murchison, in his work on the ' Silurian System,' has 

 preferred to separate the Old Red-Sandstone from the superincumbent 

 strata, and to constitute for it an additional system. Since the publi- 

 cation of that work, the same author, in conjunction with Professor 

 Sedgwick, believing that the limestones and slaty and conglomerate 

 rocks of South Devon belong to the same geological period as the true 

 Old Red-Sandstone of Herefordshire, and desirous of improving the 

 nomenclature, has proposed for these variable strata the title of the 

 Devonian System. 



The following table and account of this formation is given by Pro- 

 fessor Ansted in his ' Elementary Geology': 



Old Red-Sandstone Series. 

 Herefordshire. Scotland. 



f Quartzose Yellow Sandstone. 

 Old Red Conglomerate . . . 4 Impure Limestone. 



I Gritty Red-Sandstone. 

 Cornstone . . . . . Gray Fissile Sandstone. 



, , 



Cornstone and Marl 



f Red and Variegated Sandstone. 

 J Bituminous Schist. 

 'J Coarse Gritty Sandstone. 

 [.Great Conglomerate. 



Devonian Series. 



Devonshire. Belgium.. 



Calcareous Grit and Impure Lime-/ Indurated Shale and Peammite. 



stone . . . . . \ Calcareous Shale. 

 Red Flagstone .... Lower Limestone of Belgium. 

 Calcareous Slate and Plymouth f Hard Siliceous Beds and Con- 

 Limestone . . . .\ glomerates. 



The fossils of this period include many species of corals, Encrinites, 

 and shells. There are also a number of remains of fishes, some of very 

 great interest from the remarkable peculiarities of form and structure 

 which they present. Many of these are small, but others of gigantic 

 proportions. [FisH.] 



The Old Red-Sandstone of England and Wales consists of various 

 strata of limestone, marl, and sandstone, alternating with great thick- 

 nesses of conglomerate, which often pass upwards into overlying 

 sandstones ; and the series is expanded over a considerable portion of 

 our island, rising into lofty mountains, occupying extensive plains, 

 and developed to an enormous thickness. 



In North Wales, although the Old Red-Sandstone retains its general 

 character, we find it inferior in thickness and importance to its deve- 

 lopment in Herefordshire and South Wales. It again increases however 

 as we advance still farther northward into Westmoreland and Cumber- 

 land, where it appears as an irregular conglomerate. In this part of 

 England its largest development is near the foot of Ullswater, and it 

 rises into a succession of round-topped hills several hundred feet high, 

 the beds being of great thickness. No true passage is there discernible 

 into the overlying limestone!!. 



The loftiest points occupied by this deposit are the Vans of Caer- 

 marthen and Brecon, the former 25'JO and the latter 2500 feet above 

 the level of the sea. These hills are made up of a conglomerate com- 

 posed of white quartz pebbles embedded in a red matrix ; and it is 

 this quarterage conglomerate which gives its name to the uppermost 

 group of the formation. 



