Class I. Thallogenae.—Thallogens.

Anandrae, Link; Acotyledoneae, Agardh; Homonemeae, Fries; Cryptophyta, Link; Thallophyta, Endlicher; Amphigenae, Ad. Brong.

Characters.—Substance of the plant composed chiefly of cellular tissue, devoid of spiral vessels. Cuticle destitute of stomata, or breathing pores. Stem and leaves undistinguishable. No opposition of stem and root.

This class includes three orders:—

I. Thallogens nourished through their whole surface by the medium in which they vegetate:	Aquatic:	1. Algae.
	Aërial:	2. Lichenes.
II. Thallogens nourished through their thallus (spawn or mycelium) by juices derived from the matrix:	3. Fungi.

The Elements of Materia Medica and Therapeutics, Vol. II, 3th American ed., was written by Jonathan Pereira in 1854.