CRYPTOGAMS 



297 



FIG. 425. Asea- 

 woc <} J h ^ road - cx ~ 



paiided thallus. 



Beginning with the simplest forms, cryptogams are grouped 



in three great orders : - 



333. I. Thallophytes, or thallus plants. This group takes 



its name from the thallus structure that characterizes its 



vegetation. In its typical form, a thallus is 



a more or less flat, expanded body, of which 



the lichens and liverworts offer familiar ex- 



amples among land plants, and the kelps and 



laminarias among seaweeds. It may be of 



any size and shape, however, and sometimes 



consists of a mere filament, as in the com- 



mon brook silk, or even of a single cell (Fig. 



429). The term is applied in general to the 



simplest kinds of vegetable structure, in 



which there is no differentiation of tissues, 



and no true distinction of root, stem, and 



leaves. While it is not peculiar to the thal- 



lophytes, it has attained its most typical development among 



them, and the name is therefore retained as distinctive of 

 that group. It embraces two great divi- 

 sions, the AlgSB and Fungi. The first 

 includes seaweeds and the common fresh- 

 water brook silks and pond scums, be- 

 sides numerous microscopic forms whose 

 presence escapes the eye altogether, or is 

 made known only by the discolorations 

 and other changes caused by them in the 

 water. To the fungi belong the mush- 

 FIG. 426. Anthoce- rooms and puff balls, the molds, rusts, 



ros, a liverwort with flat, m iid e ws, and the vast tribe of micro- 



spreading thallus. . i i 



scopic organisms called bacteria, which 

 are so .active in the production of fermentation, putrefac- 

 tion, and disease. 



334. II. Bryophytes, or moss plants.- This group likewise 

 contains two main divisions, Mosses and Liverworts. Famil- 

 iar examples of the latter are the flat, spreading green plants, 



