Defn: See Thallous.
THALLIUM
Thal"li*um, n. Etym: [NL., fr. Gr. green line in its spectrum.]
(Chem.)
Defn: A rare metallic element of the aluminium group found in some minerals, as certain pyrites, and also in the lead-chamber deposit in the manufacture of sulphuric acid. It is isolated as a heavy, soft, bluish white metal, easily oxidized in moist air, but preserved by keeping under water. Symbol Tl. Atomic weight 203.7.
THALLOGEN
Thal"lo*gen, n. Etym: [Gr. -gen.] (Bot.)
Defn: One of a large class or division of the vegetable kingdom, which includes those flowerless plants, such as fungi, algæ, and lichens, that consist of a thallus only, composed of cellular tissue, or of a congeries of cells, or even of separate cells, and never show a distinction into root, stem, and leaf.
THALLOID
Thal"loid, a. Etym: [Thallus + -oid.] (Bot.)
Defn: Resembling, or consisting of, thallus.
THALLOPHYTA
Thal*loph"y*ta, n. pl. [NL. See Thallophyte.] (Bot.)
Defn: A phylum of plants of very diverse habit and structure, including the algæ, fungi, and lichens. The simpler forms, as many blue-green algæ, yeasts, etc., are unicellular and reproduce vegetatively or by means of asexual spores; in the higher forms the plant body is a thallus, which may be filamentous or may consist of plates of cells; it is commonly undifferentiated into stem, leaves, and roots, and shows no distinct tissue systems; the fronds of many algæ, however, are modified to serve many of the functions of the above-named organs. Both asexual and sexual reproduction, often of a complex type, occur in these forms. The Thallophyta exist almost exclusively as gametophytes, the sporophyte being absent or rudimentary. By those who do not separate the Myxophyta from the Tallophyta as a distinct phylum the latter is treated as the lowermost group in the vegetable kingdom.
THALLOPHYTE
Thal"lo*phyte, n. Etym: [Gr. (Bot.)