THE CLASSIFICATION OF FOSSIL PLANTS 
or on dead plant or animal substances. To them belong 
the lowest known plant organisms like the bacteria and 
the amoebae, as well as higher types like the mushrooms, 
which grow in damp, moist places on decaying wood and 
leaves. Neither fungi nor algae have tissue; they are 
merely threads or flat plates of cells; even the most com¬ 
plex mushroom is a felt-like structure of cell-threads 
without real tissue. 
Among the algae, there are some enormous forms like 
the kelps and the tangs of the ocean, which grow to 
great length and float on the surface of the water. They 
are, none the less, primitive in structure and could never 
support their own weight in the air. Algae live in the 
ocean along the shelves of the continents or in stagnant 
bodies of fresh water. 
Another well-known member of the thallophytes is the 
lichen. They are an association of fungi and algae in 
which two kinds of plants live together, to their mutual 
advantage, in the relationship known as symbiosis. The 
algae produce the chlorophyll, and the fungi give support 
to the algae, getting nourishment from them. 
The next great stem is that of the moss plants or 
bryophytes. They are a slightly higher type of plant- 
life, and are accustomed to live on land. They are divided 
into the large groups of Hepaticae or liverworts, and 
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