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505 



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plants; amongst dicotyledons they are found chiefly in 

 quick-growing plants, as Cucurbitacese. 



Moniliform vessels have successive dilatations and con- 

 tractions of the tube, and a perfect spiral fibre in their in- 

 side. It has been proved by Slack that these vessels de- 

 rive their peculiar form from accidental compression. They 

 are found in the knots of trees where branches are given 

 off, in roots, and other parts where they meet with obsta- 

 cles to their longitudinal development. 



Spurious fibro-vascular tissue includes scalariform, 

 porous, and dotted vessels. The spurious vessels are not 

 found in the tissues of young plants, and are either de- 

 veloped after the appearance of the genuine spiroids, or 

 are formed from them. Meyen maintains the latter view, 

 but Link and other botanists are still inclined to give to 

 some of the barred and dotted tissues an original develop- 

 ment. In the medullary sheath, the spurious spiroids are 

 never found in the young plant, although they are some- 

 times in the albumen and bark ; but it is not necessary 

 that a pure spiral fibre should always be visible previous 

 to its being converted into some one of the forms of spurious 

 spiroids. If in a very large number of cases there is evi- 

 dence that lings, bars, and dots are formed from the 

 metamorphosis of spiral fibres, we may fairly conclude that 

 in those cases where no observation proves to the con- 

 trary, the same effect? are to be attributed to the same 

 cause. 



Scalariform vessels consist of tunes mostly prismatical, 

 with spots on their walls resembling bars or straps. These 

 bars are placed one above another in a ladder-like form ; 

 hence their name. They are abundant in ferns, where the 

 prismatic form of the spfroid is most frequently seen. 



Porous vessels are tubes with bright spots upon their 

 walls (A, i, Fig. 4) ; they constitute the continuous Both- 

 renehyma of Lindley. They are found in greatest abun- 

 dance in the old wood of Coniferae, in the same positions 

 where spiral vessels are found, in the young wood, and 

 also in the roots of plants. The dots constituting what 

 were erroneously thought to be pores, have the same 

 character as those of fibre-cellular tissue. These vessels 

 often attain a great size, measuring as much as a quarter of 

 a line in diameter. 



Dotted vessels constitute the tissue which has been called 

 ' glandular u-O'idi/ tisstn;' and to which Meyen applies pe- 

 culiarly the term Prosenchyma. (F/g. 3 ; t>, Fig. 4.) The 

 dotted vessel, like the dotted cell, has dark spots on the in- 

 side of its membranous walls ; but in addition to the dot 

 there is also a circle. This dot does not appear to be formed 

 by the remains of a pai tly-absoibed fibre, or the crossing of 

 the fibres, as in some of the forms of porous cel ! s and 

 vessels, but from the sinuous flexures of one or more 

 fibres uniting together and forming between them a little 

 cavity or depression : this is attended with depression of 

 the external membrane, which gives the appeaiance of 

 the larger circle surrounding the depression. (Fig. 2; 

 b, Fig. 4.) These phenomena make their appearance veiy 

 early in the tissues of Coniferous plants ; but if buds and 

 very young plants are examined, the sinuous spiral vessels, 

 called by Link vasa tfiroida Jlbrota, may be easily seen. 



Function. The function of the tissues of vegetables is 

 not so varied as their forms have led botanists to suppose. 

 As a summary of them we give the following. In the 

 simple cell we have the type of all the other tissues, and 

 in the lowest forms of plants it alone performs all the 

 functions of the higher plants. The cell of the Ustilago 

 absorbs nutriment from without : this nutriment undergoes 

 the changes that fit it for becoming a part of the structure 

 of the cell. This is the process of nutrition. Within this 

 cell another is generated, which is capable of performing 

 the same functions as its parent. This is reproduction. 

 As we ascend in the scale of organization of plants, the 

 structure becomes more complicated. Cells are accumu- 

 lated together ; some simply absorb sap, others expose the 

 sap to the atmosphere ; whilst others separate peculiar 

 secretions, and another set are employed as the depositaries 

 of these secretions. As the functions of the plant become 

 more localised in the organs called leaves and flowers, 

 tissues strong enough to bear them up in the air are re- 

 quired, and the cells are elongated and strengthened by 

 an increase of thickness in their membrane, and woody 

 tissue is formed. Where the same objects are required, 

 and at the same time space for a large quantity of fluid to 

 pass through the cells, fibre is generated within the mem- 

 P. C., No. 1551. 



brane ; and for this reason fibre-cellular, and especially 

 fibro-vast-ular, tissue is found abundant in succulent 

 plants, and in those which require a large supply of mois- 

 ture. These tissues are absent, or very small in dry plants, 

 as well as those which are constantly immersed in water. 

 In the higher plants the conveyance of the prepared juices 

 from one part of the plant to another is provided for by 

 the Laticiferous tissue. It is upon the cell of the ovule 

 in the Dicotyledonous and Monocotyledonous plants that 

 the mysterious dynamic agency is exerted by another cell 

 from the anther, the result of which is the pioduction of 

 another plant, similar to the one from which it is deve- 

 loped. It will thus be seen that all the tissues ot plants 

 partake more or less of the functions of the simple cell, 

 which, as the fundamental form of vegetable organization, 

 performs in all cases the most impoitant functions. It is 

 not so much by a difference in the form as by a difference 

 in the function of particular cells that the complicated 

 organs of the highest plants are distinguished fiom one 

 another. 



(The principal works consulted in preparing this article 

 have been Meyen, Pflanzen-Physiulogie, band i. ; Link, 

 E'ementa Philosophies Botanical; De Candolle, Organo- 

 graphie Vggttale ; Lindley, Elements of Botany, and Intro- 

 duction to Botany ; Guadichaud, Rccherches stir I'Organo- 

 graphie, $c. des Vgggiaus; Bischoff, Lehrbuch der Botanik. 

 Papers : Quekett, On the Development of Vascular Tissues 

 of Plants, in ' Trans. Microscop. Soc.,' vol. i., 1842; Kip- 

 pist, On the Spiral Cells of Acunthucea?, ' Linnaean Trans- 

 actions,' vol. xix., 1842 ; Schleiden, Beitr'dge zur Phylo- 

 genesis, Miiller's ' Archiv,' 1838; Willshire, On Vegetable 

 Structure, ' Annals of Natural History,' vol. ix. : Sc-hultes, 

 Sur la Circulation duns les Plantes ; Lankester, On the 

 Origin of Wood, ' Ann. of Nat. Hist.,' 1840.) 

 TITANIC ACID. [TITANIUM.] 



TITA'NIUM. This metal was first recognised by 

 Mr. Gregor, in 1701, as a distinct substance ; he detected it in 

 a black sand found in the bed of a rivulet near Menaccan 

 in Cornwall. In 1795 Klaproth discovered it in some 

 other mineials, and he gave it. the name it now bears. The 

 properties of titanium were not however satisfactorily de- 

 termined until 1822, when Dr. Wollastou examined and 

 described it as it occurred in its perfect metallic and n\s- 

 tallized state, in the slag of an iron-furnace at Merthyr 

 Tydfil in South Wales. The form of the crystals is the 

 cube ; their colour resembles that of bright copper ; they 

 are sufficiently hard to scratch rock-ciystal, and their spe- 

 cific gravity is 5-3. 



Titanium is not acted upon by nitric, hydrochloric, or 

 sulphuric acid, either cold or hot, concentiated or di.uted; 

 aqua regia, or nascent chlorine, is also powerless, but a 

 mixture of nitric and hydrofluoric acid dissolves titanium : 

 for fusion an extremely high tempeiature is required: 

 when strongly heated with nitre, titanium is oxidized and 

 rendered soluble in hydrochloric acid, and it is precipitated 

 from solution by the alkalis in the state of a while oxide. 



We shall now describe the principal minerals known to 

 contain titanium, except PYROCHLORE, POLYMIGNITE, ZIR- 

 CON IA, &c., which aie described under these heads. 



Anatase, Octaedrite, or Oisanite. This is protoxide of 

 titanium nearly pure. It occurs in attached and imbedded 

 acute octohedral crystals. Primary form a square prism. 

 Cleavage parallel to the terminal planes, and to those of 

 the octohedron. Fiacture conchoidal. indistinct. Hard- 

 ness : scratches phosphate of lime, and is scratched by 

 quartz. By friction becomes negatively electrical, and 

 when heated gives out a reddish" yellow phosphorescent 

 light. Colour, various shades of brown, more or less dark, 

 sometimes indigo blue. Streak white. Lustre adaman- 

 tine. Translucent, transparent. Specific gravity 3-826. 

 It occurs in Cornwall, in Dauphiny, at Bourg d'Oisans, 

 in Spain, Switzerland, and some other places. It consists 

 almost entirely of oxide of titanium, probably the prot- 

 oxide. 



Rutile, or Titanite : Peroxide of Titanium, or Titanic 

 Acid. Occurs crystallized and in crystalline masses. Pri- 

 mary form a square prism. Cleavage parallel to the lateral 

 planes. Crystals frequently geniculated. Fracture uneven. 

 Hardness : scratches glass, and sometimes quartz. Colour 

 red, reddish brown, and occasionally yellowish. Streak 

 very pale brown. Lustre adamantine. Translucent, trans- 

 parent, opaque. Specific gravity 4'249 to 4-4. Occurs not 

 unfrequently inclosed in quartz, in fine red filamentous 



VOL. XXIV.-3 T 



