264 ESSENTIALS OF BOTANY 



work of pliotosynthesis. Fungi are therefore destroyers of 

 food, and {like animals) on the ivhole lessen the total amount 

 of organic matter on the earth, while green plants tend to 

 increase it. In fungi, formation of fat or oil, especially as 

 reserve material, takes the place of the starch making so 

 common in plants with chlorophyll. 



As regards their mode of life, fungi may be roughly di- 

 vided into three groups : (1) pure saprophytes; (2) plants 

 which are saprophytic or parasitic according to circum- 

 stances ; (3) plants which can only reach their full de- 

 velopment as parasites. Several of the classes of fungi 

 mentioned in Sect. 305 contain representatives of all three 

 of the groups given above. The common mushroom is 

 a familiar example of the first group, Armillaria mellea 

 (Fig. 185) is a member of the second group, and the rusts 

 of Figs. 181—183 belong to the third group. 



