The Lower Plants 71 



THE FUNGI 



The algae are the plants which may be consid- 

 ered to show the most perfect adaptation to aquatic 

 life, the aquatic ferns and seed plants being proba- 

 bly the descendants of terrestrial forms which have 

 reverted to the aquatic habit. There are, however, 

 certain plants of somewhat heterogeneous nature 

 which differ very widely in their habits from the 

 normal plants and have become extraordinarily mod- 

 ified so that it is practically impossible to trace their 

 ancestry. These are the Fungi, which include such 

 familiar forms as mushrooms, molds, mildews, rusts, 

 an enormous assemblage of species, second in num- 

 ber only to the flowering plants. The Fungi never 

 possess chlorophyll, and so far as is known are quite 

 unable to assimilate CO 2 for food, and hence they 

 are dependent upon organic matter for their carbon, 

 just as animals are; but some of them, like the 

 nitrogen bacteria, can use the atmospheric nitrogen. 



A bit of bread exposed to moist warm air 

 soon becomes covered with a growth of mold, which 

 an examination will show to include a number of 

 quite different species. These arise from tiny spores 

 which germinate upon the moist bread and quickly 

 produce a tangled, webby mass of fine threads which 

 ramify through the bread, breaking down the starch 

 by means of the ferments or enzymes secreted by 

 the invading fungus filaments, and using the starch 

 for food. Similarly, a mushroom growing in a 



