107S 



TISSUES, VEGKTABLE. 



TITANIUM. 



107 



nib in the matter from which they are formed bating greater opacity, 

 and not transmitting the light so freely. 



Vascular, or Tubular Timme, consists of conlinuoug tubes of dimple 

 membrane, and comprehends the woody and the latlciferous tissues. 

 On the ouc hand they are distinguished by their length from the forms 

 of cellular tissue, and on the other hand by their plane membrane 

 from thoee tissues of which fibre forms a constituent element 



Pleurenchyma, or Woody Tissue (Vasa Fibrosa of Link, and Faser- 

 gefaase, German), is found abundantly in the wood, and especially the 

 liber, of all plants. It is composed of very long, thin, tough, trans- 

 parent, membranous tubes. No bars or dots are teen in their walls, 

 although when they cross each other the points at which they touch 

 may be taken for such markings. They taper acutely to each en<\, and 

 do not appear to have any communication ouc with the other, although 

 they are occasionally seen with open extremities, which Slack supposes 

 to arise from the breaking off of one fibre where it was united to 

 another. In the wood and bark of Dicotyledonous Plants they are 

 frequently mixed with Prosenchyinn, and in Monocotyledonous Plant* 

 with Parenchyma. They grow by increasing in length both above and 

 below. Their diameter varies from 1-lSOth to l-3000th of an inch. 

 The walls increase in thickness by the deposition of cellulose. Their 

 form is mostly cylindrical, but in Oycai revoliita Link has observed 

 them assuming a prismatic form. 



The tubes of woody tissue are very tough, and will resist consider- 

 able force without breaking. It is on this account that they are used 

 extensively in the manufacture of cloths of various kinds. The plants 

 used most commonly for this purpose are the hemp and flax. The 

 fibres of Tilia, Daphne, Lagella, and of many of the plants of the 

 order of ifalractct, are used for making mats, cordage, whips, Ac. 

 The following is a comparative statement of the relative strength of 

 silk and some woody fibre : 



Silk supported a weight equal to , 34 



New Zealand Flax 23* 



Hemp 16i 



Flax 11J 



Pita Flax (Agate Americana) . T 



Woody tissue gives firmness and tenacity to the plant, and assists in 

 conveying the sap from the roots to the leaves. 



Vascular Tissue occurs in bundles, that is, several tubes lie close 

 together in a bundle, and are surrounded by cellular tissue. Schleiden 

 describes three kinds of bundles : 1. Simultaneous, in which all the 

 fibre* are developed at the same time, as seen in the Ferns. The next 

 are successive, in which the centre fibres are first developed, and thoee 

 in the circumference after. These are divided into 2. Definite, in 

 which the bundles, after having grown, are closed around by cellular 

 tissue, as are seen in Monocotyledons. 3. Indefinite, in which the 

 bundles do not cease to develop in the direction of their growth, as 

 occurs in the bundles of woody tissue found in the stems of Dicoty- 

 ledonous or Exogenous Plants. The mode of growth of these two 

 last forms of vascular tissue seems to determine the forms of Monoco- 

 tyledoDous and Dicotyledonous stems. 



Cinencbyma, or Laticiferous Tissue, consists of tubes which are 

 mostly branched and anastomosing ; their walls are exceedingly deli- 

 cate in young plants, and thicker in old ones ; and they are characterised 

 by conveying a fluid called the latex, which differs from the sap in 



other parts of the plant. The older 

 botanists, SpigelhiK, Malpighi, and 

 Grew, described them, but they were 

 generally confounded with woody 

 tissue, till they were investigated by 

 Schultes. In older writers they are 

 called Vasa Propria or Peculiaria; 

 by Link, Vasa Opophora. 



They are regarded by many ob- 

 servers a* intercellular passages, iu 

 the course of which organic matters 

 have been deposited, giving them the 

 character of vessels with walls. The 

 phenomena described by Schultes 

 are most easily seen in plants con- 

 taining a milky juice, as the Euphor- 

 biactcf. Their most remarkable cha- 

 racter is the possession of branches 

 communicating with each other, thus 

 giving them the appearance of the 

 capillaries in animals. (Fig. 3). The 

 history of their development is not yet sufficiently made out to give 

 them a claim to be considered as a genuine form of vegetable tissue. 



Fibro-Vascular Tissue, or Trachenchyma (Vasa Spiroidea of Link), 

 con-inU of tubes, in the inside of wbioh spiral fibres are generated. 

 The fibres of this tissue are subject to metamorphosis, the consequence 

 of which is, the tubes present the appearances of rings, bars, and 

 bright and dark spotsi 



The tubes consist of a very delicate membrane, which is montly 

 cylindrical ; it may however assume a prismatical form when the tubes 

 are in bundles and closely pressed together, as in Ferns and many 

 Monocotyledonous Plants. The fibres generated in this tissue are 

 mostly compressed, and wind up the sides of the tube in a spiral form. 



Fif. 3. 





Fig. 4. 



When the membrane is broken, the fibre in most care* may be 

 unrolled. It is in the younger tubes that this it most easily effected ; 

 as in the older tubes those changes go on which connect the membrane 

 and the fibre firmly together, and convert the latter into bar?, 

 Ac. The number of fibres included in a tube varies; it is frequently 

 single, but in some instances as many as 22 have been counted. They 

 have no fixed direction ; some pans from right to left, others from left 

 to right Some difference of opinion baa existed as to whether tho 

 fibres are tubular or not Schleiden says in most instances they are 

 solid, but where they are formed from Urge globules of jelly they 

 appear to be tubular in both vascular and cellular tissue. 



Link divides fibro-vascular tissue into genuine and spurion- 

 former includes all those vessels which possess perfect fibres. The 



principal forms of these are 

 the spiral, annular, and mo- 

 niliform vessels. The spiral 

 vessel consists of a tube, in 

 which one or more fibres run 

 continuously along its sides 

 from one end to the other 

 (fig. 4, d, e, /.) When tho 

 fibres are single, they are 

 called simple ; when there is 

 more than one, compound. 

 The spiral vessels are most 

 abundant in young plants, 

 as their character becomes 

 changed by age. When the 

 fibres adhere to the sides of 

 the membrane, they ore said to be closed. The spiral vessel was at 

 one time considered a very important tissue, performing especial vital 

 functions. From the circumstance of air being frequently found in 

 them, and this air containing a larger quantity of oxygen than the atmo- 

 sphere, they were supposed to carry on the function of respiration. 



Annular Vessels or Ducts consist of tubes with perfect rings of 

 fibre on their sides. (Fig. 4, jr.) These are evidently formed from tho 

 interruption of the spires, and the union of the broken ends, as they 

 are frequently found present with a spiral fibre in the (same tube. 

 They are mostly larger than the spiral vessels, and the fibre is also 

 thicker : they are very abundant in Monocotyledonous Plants; amongst 

 Dicotyledons they are found chiefly in quick-growing plants, as C'ucitr- 

 bitacea. 



Moniliform Vessels have successive dilatations and contractions of 

 tho tube, and a perfect spiral fibre in their inside. It has been proved 

 by Slock that these vessels derive 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 obstacles to 

 their longitudinal development. 



Spurious Fibro-Vascular Tissue includes Scalariform, Porous, and 

 Dotted Vessels. The spurious vessels are not found iu the tissues of 

 young plants, and are either developed after the appearance of the 

 genuine spiroids, or are formed from them. 



Scalariform Vessels consist of tubes mostly prismatical, with spots 

 on their walls resembling bars or straps. These bars ore placed one 

 above another in a ladder-like form ; hence their name. They are 

 abundant in ferns, whero the prismatic form of the spiroid is most 

 frequently Been. 



Porous Vessels are tubes with bright spots upon their walls (tiy. 4, 

 h, i); they constitute the Continuous Jiotbrenchyma of Lindley. They 

 are found in greatest abundance iu the old wood of Cmifera, iu the 

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

 also in the roots of plants. 



Dotted Vessels constitute the tissue which has been called Glandular 

 Woody Tissue, and to which Meyen applies peculiarly the term Pros- 

 enchyma. (Fig. 3 ; Jig. 4, b.) The dotted vessel, like the dotted cell, 

 has dark spots on the inside of its membranous walls ; lint iu addition 

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

 by the remains of a partly-absorbed fibre, or the crossing of tho fibres, 

 as in some of the forms of porous cells 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 appearance of 

 the larger circle surrounding the depression. (Fig. 2 ; fig. 4, i.) These 

 phenomena make their appearance very early in tho tissues of Coni- 

 ferous plants; but if buds and very young plants aro examined, tho 

 sinuous spiral vessels, called by Link Vasa Spiroida Fibrosa, may be 

 easily seen. 



For information on the functions of these tissues, see the articles 

 CELLS; SAP; KKI'IIOUUCTION i.v PLAKTS AND ANIMALS. 



(Mohl, On the Vegetable Cell, translated by Henfrey; Schleiden, 

 Principle! of Scientific Botany, translated by Laukester; Link, Ei< 

 Philoio]>hwe Botanica ; Meyer, Pflanzm I'hynologu ; Unger, Botanical 

 tetteri, translated by Paul; Brauu, fltjuvcneiccncc in Nature, translated 

 for the Hay Society.) 



TITA'NIUM. This metal was first recognised by Mr. Gregor, in 

 1791, as a distinct substance. Ho detected it in a black sand fuund in 

 the bed of a rivulet near Menaccan in Cornwall. In 1795 Klaproth 

 discovered it in some other minerals, and he gave it tho name it now 



