"WHAT ARE LICHENS ? 27 



of cheese, in tanning, and in tlie making of butter; all 

 are familiar with processes of fermentation. These 

 bacteria, wlietlier indifferent, harmful or beneficial, 

 and the producers of fermentation, belong to the 

 fungi. 



It is also generally known that fungi are either 

 saprophytic or parasitic, that is, they require organic 

 food obtained from dead or living organisms. In this 

 they differ markedly from chlorophyll-bearing plants, 

 as already indicated. Scientists have however deter- 

 mined that fungi were originally chlorophyll-bearing 

 and hence able to assimilate inorganic food ; in other 

 words, fungi are algae which have lost their chlorophyll 

 and the functions pertaining thereto. How did they 

 come to lose their chlorophyll ? The history of this 

 change is, perhaps, something as follows : Many ages 

 ago certain of the algse accidentally came in contact 

 with higher plants, from which they absorbed some of 

 the more soluble food-substances. The association re- 

 duced the amount of work to be done by the chloro- 

 phyll of the parasite ; as the association continued the 

 morphological and physiological changes in the alga 

 tended toward a more and more marked parasitism. 

 Every one is familiar with the fact that inactivity of 

 an organ causes it to become dwarfed and more or less 

 functionless. Chlorophyll became extinct in these 

 parasitic algae simply because it was functionless : all 

 of the organic food was prepared and supplied by the 

 host. This change was by no means sudden ; it re- 

 quired many ages to produce the change from bright 

 green alga to colorless fungus, or, in other words, to 



