274 FOUNDATIONS OF BOTANY 
dyes. ‘Iceland moss” is a lichen used for food, and a 
finely branching form, growing in extensive mats on the 
soil, serves as food for the reindeer and is known as 
“ reindeer moss.” 
Most lichens grow on the bark of trees, on rocks, or soil 
where they have little moisture except during rainfall, 
but some grow where they are constantly wet. Some of 
the latter are gelatinous. Most of the conspicuous lichens 
are foliaceous or else have a thallus composed of branch- 
ing, cylindrical, thread-like portions. But many species, 
often less conspicuous, are crustaceous, growing as if 
they formed part of the bark or rock to which they are 
attached. 
332. Fungi.— The yeasts, moulds, rusts, mildews, and 
mushrooms represent an immense group of plants of which 
about forty-five thousand species are now known in the 
world. ‘They range from the very simple to quite com- 
plex forms, growing as saprophytes or parasites under a 
great variety of conditions. Their structure and life 
history are so varied as to constitute a long series of divi- 
sions and subdivisions.’ Chlorophyll is absent from fungi, 
and they are destitute of starch, but produce a kind of 
cellulose which appears to differ chemically from that of 
other plants. Unable to build up their tissues from car- 
bonic acid gas, water, and other mineral matters, they are 
to be classed, with animals, as consumers rather than as 
producers, acting on the whole to diminish rather than to 
increase the total amount of organic material on the earth. 
1See Strasburger, Noll, Schenk, and Schimper’s Text-Book of Botany, 
pp. 340-381 incl., also Potter and Warming’s Systematic Botany, p. 1, and 
Engler’s Syllabus der Pflanzenfamilien, Berlin, 1898, pp. 25-47. 
