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Webster 1913 Edition
Thallogen
Thal′lo-gen
,Noun.
[Gr. [GREEK] young shoot or branch, frond +
-gen
.] (Bot.)
One of a large class or division of the vegetable kingdom, which includes those flowerless plants, such as fungi, algae, 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.