42 ELEMENTARY STUDIES IN BOTANY 



35. Economic importance. It was said of Algae that they 

 are of little or no economic importance, but of very great 

 scientific importance in the history of the plant kingdom. 

 This statement may be reversed for Fungi. They are of 

 little scientific importance in the history of the plant king- 

 dom, but of very great economic importance. In denning 

 parasites, it was stated that they induce disease, and when it 

 is realized that these plant parasites are responsible for many 

 diseases that ravage crops, domesticated animals, and the 

 human population, it would be hard to exaggerate their 

 economic importance. It is on account of this importance 

 that the parasitic fungi have received so much attention, for 

 they represent an enemy against which men must always 

 be on guard. 



On the other hand, the work of the saprophytes is often 

 beneficial. They may be regarded as natural scavengers, 

 decomposing dead bodies and organic waste into their con- 

 stituent elements or inorganic compounds. Advantage is 

 taken of this process in various manufactures, such as the 

 manufacture of alcohol from sugars, the fermentation of fruit 

 juices in the manufacture of wines, the " raising " of bread 

 dough by yeasts, etc. 



36. Origin of Fungi. It is a common belief that Fungi 

 are Alga3 that have lost the power of food-manufacture. 

 Some Algae and Fungi resemble one another so closely in 

 structure that this belief seems reasonable ; but most Fungi 

 differ so much from all known Algae that such a connection 

 does not seem convincing. It is easy to understand how 

 Algae might lose the power of food-manufacture if exposed 

 to an available food supply. For example, certain Algae 

 inhabit cavities in the bodies of green plants, and the food 

 manufactured by these plants might be available for the Algae, 

 which might thus gradually become dependent. 



Perhaps the best reason for believing that Fungi are 

 degenerate Algae is that probably the two groups existed 



