THE LICHEN 113 



regions, frequently in the form of cups, called apothecia. 

 Draw habit sketches. 



B. Section in pith with a razor a medium-sized fruit (first 

 moistened). Draw first an outline sketch, showing the rela- 

 tion of parts, and then details. Note : 



1. That there are two elements in the lichen : (a) green or 

 blue-green cells ; (h) colorless regions made up of filaments 

 more or less densely interwoven. 



2. Study in detail the green or blue-green cells under h.p., 

 comparing their structure with the algal types that have 

 been studied. 



3. Examine the colorless regions, comparing their structure 

 with such types of fungi as have been studied. 



4. Study in detail the fruiting surface. Is it algal or fun- 

 gal in character, and to what types is it clearly related ? 

 Draw carefully its structure. 



C. Study from sections the strictly vegetative parts of the 

 lichen with reference to the distribution of the parts com- 

 posing it, and especially the structure of the lower surface 

 where it comes in contact with the substratum. 



D. Search for scales, called soredia, on the surface of some 

 lichens. These scales contain algal cells inclosed in a net- 

 work of hyphiE, and falling off the parent plant may develop 

 new lichens, thus constituting a very effective means of 

 vegetative propagation. 



Reference. Principles, Sec. 271 ; Schneider, 42. 



Questions. What are your conclusions on the structure and 

 composition of a lichen ? What are its methods of repro- 

 duction ? How do new lichens develop ? Describe the life 

 habits of lichens and their effect on such substrata as rocks, 

 trees. Under what conditions do they grow most vigor- 

 ously. How do they survive periods of drought and cold ? 

 What is the food of a lichen and how is it obtained ? How 

 do the algse benefit the fungus in the lichen ? Does the 

 alga receive equivalent benefit from the fungus ? 



