SOME TYPES OP ELOWEELESS PLANTS. 235 



partnership -which occurs both among plants and among 

 animals. The so-called lichen is really a complex colony- 

 composed of a multitude of minute fungi living in close 

 connection -with certain thread-like algae. The partnership 

 between the two kinds of plants is not an especially one- 

 sided affair ; though the algae are the principal breadwinners 

 of the firm, their association with the fungi enables them to 

 live in situations and under conditions that would be fatal to 

 the algae alone. 



290. Reproduction in Fungi. — The reproductive processes 

 in fungi are so various in their character, and involve so 

 much microscopical study, if they are to be clearly under- 

 stood, that it would require many chapters to describe them. 

 The examples already considered in the cases of yeast and 

 the moulds must be allowed to stand as representatives of 

 the great number of interesting types that offer themselves to 

 the student of this department of cryptogamic botany. 



THE STTXDY OF PIGEON-WHEAT MOSS.i 



291. OcrMrrence. — This moss, Fig. 202, is -widely distributed over 

 the surface of the earth, and some of Its species are among the hest- 

 known mosses of the northern United States. Here it gro-ws commonly 

 in dry pastures or on hillsides, not usually in densely shaded situations. 



292. Form, Size, and General Characters. — Study several specimens 

 which have been pulled up by the roots.^ Note the size, general form, 

 color, and texture of all the parts of the plants examined. Some of them 

 probably bear ur-as or spore-capsules like those shown in Fig. 202, while 

 others are without them. Sketch one plant of each kind, about natural size. 



What difference is noticeable between the appearance of the leaves in 

 those plants which have spore-cases and those which have none ? Why 

 is this ? 



^ Polytriclnnn commune. Tliis is selected as one of the largest and commonest of 

 mosses. If any other genus is more readily obtainable, the teacher may as well use 

 it. For an excellent account of the structure and physiology of mosses, consult 

 Bennett and Murray's Cryptogamic Botany. For the determination of species, see 

 Lesquereux and James' Mosses of Kortli America. 



2 Fresh specimens are best, but dried ones will do nearly as well. 



