EXERCISE 91 

 A FUNGUS PARASITIC ON AN ALGA 



Materials. Lichens may be readily found on the bark of trees, 

 on fences, on stones, or on the soil. (See textbook illustrations for 

 assistance in identification.) Common forms are greenish gray, but 

 some are almost black and a few are yellow or orange. 



Directions for work. Place a fragment of a lichen on a glass 

 slide and tease it to pieces with a needle. Mount in water and 

 examine with a hand lens, or, better, with a microscope. You 

 should be able to make out small green cells and colorless fila- 

 ments. The green cells are algae, which may be one-celled, like 

 Pleurococcus, or the cells may be joined into chains or filaments. 



How could the alga secure food and water ? How would 

 the fungus secure these necessities? Compare the condition of 

 lichens after a rain with the condition of the same plants during 

 a dry period. What seems to be the relation between the fungus 

 and the alga? 



. Study and describe as many kinds of lichens as you are able 

 to find. The cups found on some of them are the fruiting bodies. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 235-239. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 247-251. 



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