THE FUNGI 165 



Although the fungi, as a class, are dependent 

 for their nourishment on substances which 

 have originated from other living things, 

 they differ a good deal among themselves as 

 to the kind of food material they can use. 

 Some are dependent on the living bodies of 

 animals or plants, and then we call them 

 parasites. Others live on dead or decaying 

 remains, and are commonly termed sapro- 

 phytes. The saprophytes are a very extensive 

 class, and include many species that can live 

 on relatively simple organic residues such as 

 sugar, organic acids, and so forth. But these 

 simpler feeders are connected with more 

 obviously saprophytic types by all con- 

 ceivable intermediate forms, and even the 

 distinction between saprophytes and parasites 

 is far from absolute, for many saprophytes 

 can become parasites, and vice versa. 



Now the utilisation of all food, regarded as 

 a means to an end, is connected with changes 

 in the states of energy. Complex organic 

 substances possess a considerable amount of 

 energy in a locked-up, or potential form, 

 When the food substances undergo oxidation 

 and are broken down into simpler ones, the 

 potential energy is set free as kinetic energy, 

 just as happens when a piece of coal is 

 oxidised or burnt. This kinetic energy is 

 directly available for doing work, and may 

 be utilised to boil a kettle or to build up the 

 body of a fungus. In the former case, the 

 kinetic energy is used to alter the physical 



