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. 1 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. 



1 See 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. 



