684 FUNGI : GENERAL 



they decompose organic bodies, breaking them down into simple 

 compounds which ultimately become available for the nutrition 

 of green plants. 



The fungi which feed upon the tissues of living plants or 

 animals are termed parasites, the plants or animals attacked by 

 the latter being designated their hosts or feeders; it is to the 

 activity of this class that serious diseases of farm and garden 

 crops are due. 



While mushrooms, most common ' moulds ' and many familiar 

 fungi are entirely saprophytic, others, such as the 'rust' fungi, 

 are entirely parasitic in habit and incapable of carrying on an 

 existence except when nourished by a living host No strict 

 line of division can, however, be made among fungi in respect 

 of the sources of their food, for certain species which usually 

 behave as saprophytes may become parasitic especially when 

 well-nourished : moreover, many parasites are capable of existing 

 as saprophytes for a considerable period. 



8. Parasites, such as hop-mould and vine-mildew, which develop 

 their mycelium on the external surface of their host-plants, are 

 spoken of as epiphytic, while those whose mycelia ramify through 

 the tissues of their victims are termed endophytic; examples of 

 the latter are the fungi causing 'damping-off,' potato disease, and 

 the ' rusts ' of cereals and other plants. The mycelia of endo- 

 phytic species are either intercellular or intracellular according 

 as the hyphae permeate the intercellular spaces only, or actually 

 penetrate the cells of the tissues in which they grow. 



The food needed by epiphytic parasites is usually absorbed 

 from the superficial cells of the host-plant by means of short 

 processes known as haustoria or ' suckers ' which are produced 

 at irregular intervals on their hypha; and penetrate into the 

 subjacent cells ; similar haustoria are also found on the hyphse 

 of some endophytic parasites, while in others of the latter 

 class transference of nutrient materials is carried on by osmosis 

 directly to the whole mycehura. 



