Thallium

“ It melts at 720° and decomposes rapidly above 800°, giving oxygen and thallous oxide. Thallous chloride, TlCl, is readily obtained from the solution of any thallous salt, by the addition of hydrochloric acid, as a white precipitate similar in appearance to silver chloride, like which it turns violet in the light and fuses below redness into a (yellow) liquid which freezes into a horn-like flexible mass. It is also formed when the metal is burnt in chlorine. The specific gravity of this “horn” thallium is 7.02. ”

“ It forms compounds of a lower type, TlX, besides the higher unstable type TlX3, just as mercury gives HgX2 and HgX. In the form of the thallic oxide, Tl2O3, the base is but feebly energetic, as would be expected by analogy with the oxides Al2O3, Ga2O3, and In2O3, whilst in thallous oxide, Tl2O, the basic properties are sharply defined, as might be expected according to the properties of the type R2O (Chapter XV.) . Thallium was discovered in 1861 by Crookes and by Lamy in certain pyrites. ”

“ G. W. Kahlbaum, of Basle, with great success to potassium, sodium, selenium, tellurium, cadmium, magnesium, bismuth, and thallium, while the experiments with zinc and manganese have so far been unsatisfactory. Judging by spectrum analysis, an extreme degree of purity was obtained. Thus, thirty-five ines disappeared from the spectrum of tellurium, showing, the author believes, the absence of substances which modify the spectrum of the purest metal obtainable by other processes. ”

“ The sexual generation, gametophyte, or prothallium, is always a thallus, although not always green and leaf-like (Figs. 205, 215, 222, 229, 235, etc.) It is very small, even in cases where it attains the greatest development, and consists only of parenchymatous cells. The prothallium is nourished by hair-like roots (rhizoids) and has only a transitory existence, dying soon after the fertilisation of its oosphere. ”

“ One of the Nereids.
||Tha`li*a"ce*a (?) , n. pl. [NL. See Thalia.] (Zoöl.) A division of Tunicata comprising the free-swimming species, such as Salpa and Doliolum.
Tha*li"an (?) , a. Of or pertaining to Thalia; hence, of or pertaining to comedy; comic.
Thal"late (?) , n. (Chem.) A salt of a hypothetical thallic acid.
Thal"lene (?) , n. (Chem.) A hydrocarbon obtained from coal-tar residues, and remarkable for its intense yellowish green fluorescence.
Thal"lic (?) , a. (Chem.) Of or pertaining to thallium; derived from, or containing, thallium ”

“ In some cases the individual consists of a minute simple cell which multiplies by cell-division; in others the body or thallus is made up of a number of similar units, while in a great number of forms there is a well-marked physiological division of labour, as expressed both in the external division of the thallus into distinct organs corresponding in function to the root, stem, and leaves of the higher plants, and further in the high degree of histological differentiation of the tissues. In other thallophytes, again, the thallus is a coenocyte either unseptate or incompletely septate ”

“ Thallus foliose, but smaller and thinner than that of Peltigera, and devoid of trichomatic hyphae, more or less closely attached to the substratum by rhizoids; cortex well developed on both upper and lower sides; medulla well developed (Fig. 2) ; apothecia confined to the lower side of the thallus, marginal on narrow, slightly elongated lobes, thalloid margin persistent and crenate; hypothecium usually some shade of brown; hymenium [Pg 359] usually pale below and brown above; paraphyses simple or branched; spores brown, 4-celled, 8 in each ascus. ”

“ Within the Lecideaceae, the line of evolution seems to have been in the direction of a well-developed exciple and from simpler to more complex spores. With the advance in these two directions has gone a slightly increased development of the thallus.
In structure, the thallus is crustose, and the thalli vary from inconspicuous, evanescent conditions to those which are conspicuous and sometimes even subsquamulous. Rarely the thallus extends upward as a veil which surrounds the apothecia laterally and suggests how the thalloid exciple of higher families probably arose. ”

“ No leaf-like appendages are borne on the thallus, but short glandular hairs occur behind the apex. The plant is composed throughout of very similar living cells, the more superficial ones containing numerous chlorophyll grains, while starch is stored in the internal cells of the midrib. The cells contain a number of oil-bodies the function of which is imperfectly understood. The growth of the thallus proceeds by the regular segmentation of a single apical cell. The sexual organs are borne on the upper surface, and both antheridia and archegonia occur on the same branch (fig. 3, A) . ”

“ Thallus consists of simple or branched rows of cells in which special cells known as heterocysts often occur. Reproduction by means of germ-plants or hormogonia, or by resting cells specially modified to resist unfavourable conditions.
In both families the individuals are surrounded by a gelatinous envelope, which in some genera assumes the form of a conspicuous and comparatively resistant sheath. Marine, freshwater, and aerial forms are represented among recent genera. Several species occur as endophytes, living in the tissues or mucilage-containing spaces in the bodies of higher plants. ”

“ In addition to the cell types described, it is a very common occurrence in these bulky forms for rhizoid-like branches of the cells to grow out, mostly from the cells at the periphery of the medulla, and grow down between the cells, strengthening the whole tissue, as in the Rhodophyceae. This process may result in a considerable thickening of the thallus. In many Laminariaceae the thallus also grows regularly in thickness by division of its surface layer, adding to the subjacent permanent tissue and thus forming a secondary meristem. ”

“ Fertilisation similar to that in Bryopsis occurs perhaps in Codium. They are all salt water forms.
Order 8. Valoniaceæ. The thallus is generally multicellular, without differentation into stem- or leaf-structures, but the cells are sometimes united together and form a leaf-like reticulate expansion (e.g. Anadyomene) . Zoospores are known in some, and they are then formed directly in the vegetative cells. In others (e.g. Valonia) , a mass of protoplasm, which maybe separated through the damaging of a cell, can surround itself with a cell-wall, and grow into a new plant. ”

“ For, as Pythagoras said, not every kind of wood is fit to be carved into the likeness of Mercury. If that be so, tell me who was that healthy, unblemished, intelligent, handsome boy whom I deemed worthy of initiation into such mysteries by the power of my spells. As a matter of fact, Thallus, whom you mentioned, needs a doctor rather than a magician. For the poor wretch is such a victim to epilepsy that he frequently has fits twice or thrice in one day without the need for any incantations, and exhausts all his limbs with his convulsions. ”

“ The thallus is usually encrusted with carbonate of lime; it is of a branched cylindrical form in the well-known Corallina officinalis, Linn. of the British coasts, of an encrusting and foliaceous type, in the genus Lithophyllum, and of a more coral-like form in the genus Lithothamnion. The reproductive organs occur in conceptacles, having the form of small depressed 184cavities in the thallus, or projecting as warty swellings above the surface of the plant. Asexual reproduction is by means of tetraspores formed in conceptacles resembling those containing the sexual cells. ”

“ The complete body of all Algæ and of all Thread-plants is a mass composed of simple 80 cells, which is called a lobe, or thallus. This thallus is as yet not differentiated into axial-organs (stem and root) and leaf-organs. On this account, as well as through many other peculiarities, the Thallophytes contrast strongly with all remaining plants—those comprised under the two sub-kingdoms of Prothallus plants and Flowering plants—and for this reason the two latter sub-kingdoms are frequently classed together under the name of Stemmed plants, or Cormophytes. ”

“ The growth of the thallus is chiefly intercalary. The star-like chromatophores contain chlorophyll and are coloured blue-green with phycocyan, or reddish with phycoerythrin; all these colouring matters are occasionally found in the same cell (Bangia-species) . Asexual reproduction by tetraspores, without cilia, but capable of amœboid movements.
Sexual reproduction is wanting, or takes place by the coalescence of a spermatium with a carpogonium, which is only slightly differentiated from the vegetative cells, and is devoid of a trichogyne. ”

“ Thallus, thal′us, n. a vegetative body showing little or no differentiation into leaf, stem, and root, and characteristic of the Thall′ophytes or lower Cryptogamia, including algæ, fungi, and lichens.—adjs. Thall′iform, of the form of a thallus; Thall′ine, Thallod′ic, pertaining to a thallus.—n. Thall′ogen, a thallophyte.—adjs. Thallog′enous, belonging to the thallogens; Thall′oid, Thall′ose, resembling a thallus.—ns. Thall′ōme, a thallus; Tham′nium, the branched shrub-like thallus of fruticulose lichens. [Gr. thallos, a young shoot.] ”

“ And if we look to Anaximander, the person next in order of time to Thalês, as well as to Herakleitus, we find them departing, in a great degree, even from that character which all the rest have in common, though both the one and the other are usually enrolled in the list of Ionic philosophers.
Of the old legendary and polytheistic conception of nature, which Thalês partially discarded, we may remark that it is a state of the human mind in which the problems suggesting themselves to be solved, and the machinery for solving them, bear a fair proportion one to the other. ”

“ The thallus in the vegetative condition is unicellular, and consists at the lower extremity of branched rhizoids, while the upper portion is prolonged into a stem-like structure of unlimited growth, producing, acropetally, branches and leaf-like structures. The latter have limited growth, and are separated by a cross wall from the stem, and become gametangia, or drop off. The gametes have two cilia, and are of two kinds: the female, which are green and large and the male, which are of brownish colour and smaller. Zoospores or any other method of asexual reproduction are unknown. ”

“ The lowest Hepaticae have an extremely simple vegetative structure, little more advanced than that found in some of the higher Green Algae and very much simpler than in the large Red and Brown Seaweeds, The plant-body (thallus) is always small and normally lives in very damp air, so that the demands of terrestrial life are at a minimum. It always consists of true parenchyma, and is entirely formed by the cutting off of segments from an apical cell. ”

“ Thallus a thin and scurfy, smooth or chinky, or thicker and roughened-verrucose, ash- to green-gray, or darkening crust, irregularly spread over small areas, and rarely disappearing; apothecia minute to small, 0.2 to 0.6 mm. in diameter, often numerous, black, adnate, flat and bordered by an exciple, or becoming convex with the exciple sometimes covered; hypothecium dark brown; hymenium pale, or pale below and pale brown above; paraphyses distinct, but sometimes loosely coherent; asci clavate; spores oblong-ellipsoid, 7 to 16 mic. long and 4 to 7.5 mic. ”

“ In Graphis scripta (fig. 26) the thallus is thin, somewhat membranous, smoothish, shining, greyish white, and faintly bordered with black. The lirellæ (fig. 27) are partly sunk in the bark, winding and narrow, some being simple, others branched; and they are surrounded by a raised border, formed by the thallus. The lirellæ are lined at the sides with a black (carbonaceous) layer or excip ́ulum, within which are situated the asci and paraphyses. The spores (Pl. II. fig. 29) are 8-cleft, the segments being again divided longitudinally into little spores or sporidia. ”

“ For example, in the course of his travels, he at one time visited Egypt, and while there, he contrived a very simple way of measuring the height of the pyramids. He set up a pole on the plain in an upright position, and then measured the pole and also its shadow. He also measured the length of the shadow of the pyramid. He then calculated the height of the [Pg 168] pyramid by this proportion: as the length of shadow of the pole is to that of the pole itself, so is the length of the shadow of the pyramid to its height.
Thales was an astronomer as well as a philosopher and engineer. ”

“ Only the lower, root-like part of the thallus, which penetrates the calcareous substratum survives the winter, and may grow up into a new plant. The sterile leaves, which drop off early, are dichotomously branched and formed of cylindrical cells separated from each other by cross-walls, but they are not grown together. ”

“ Each pit or circular depression (fig. 33, N) marks the position of the swollen tip of a branch.
This form of thallus represents a type which is met with in several members of the Dasycladaceae. It would carry us beyond the limits of a short account to describe additional recent genera which throw light on the numerous fossil species. For further information as to the recent members of the family, the student should refer to Murray’s Seaweeds [309] , and for a more detailed memoir on the group to Wille’s recent contribution to the Pflanzenfamilien [310] of Engler and Prantl. ”

“ The “thallus” characteristic of the Scotch Boghead has been named Pila scotica, and that of the Autun Boghead, Pila bibractensis.
In the latter form, which has been studied in more detail by MM. Renault and Bertrand, the thallus consists of about 6–700 cells, and is irregularly ellipsoidal in form, from ·189–·225mm. in length, and ·136–·160mm. broad. The surface-cells are radially disposed and pyramidal in shape, the internal cells are polygonal in outline and less regularly arranged (fig. 36, 2) . The Pila thalli make up 3⁄4ths of the mass in an average sample of the Autun Boghead. ”