CHAPTER XVI 



FUNGI AND FUNGOUS DISEASES OF PLANTS 



220. The fungi as dependent plants. In our earlier discus- 

 sion of plant nutrition it was found that green plants possess 

 chlorophyll, by means of which they make their own foods. 

 Every observant person who has had any considerable experi- 

 ence with plants has noted several or many kinds, as mush- 

 rooms and molds, that do not 

 possess chlorophyll. These 

 chlorophyll-less plants can- 

 not manufacture foods from 

 water and carbon dioxide, and 

 hence are dependent. Their 

 dependence appears in various 

 relations between them and 

 the host plants or animals 

 that supply them the requi- 

 site food. Sometimes they live 

 upon or within living plants 

 or animals, being known as 

 parasites ; or they may live 

 upon dead nutrient sub- 

 stances, when they are known 

 as saprophytes (fig. 182). 

 There are many common fungous parasites, as wheat rust, 

 potato blight, and tree-destroying fungi. Our economic crops 

 are greatly reduced in value every year through the destruc- 

 tiveness of these parasitic plants. Fungous saprophytes are 

 also very abundant, the best-known being molds, mushrooms, 

 and puffballs. In almost any deeply shaded, moist, and warm 



234 



FIG. 182. An old pine stump upon 

 which the fungus Polyporus is growing 



