1 8 Trunsaclions British Mycolngical Society. 



often one of great benefit; but bacteria have not been in- 

 cluded in the present survey. 



Saprophytism. The saprophytic relationship is the most 

 simple of all. There are no special organs of absorption or 

 excretion in fungi; the active hyph^e travel over and 

 through the dead substances — mostly wood, leaves, &c., 

 and are constituted to take up food material over their whole 

 surface. By means of ferments, in which they are pecu- 

 liarly rich, thev break up organic compounds and thus 

 render them serviceable not only to the fungus itself but 

 to the other plants. This fermentative action of fungi has 

 been made use of in many different economic processes, and 

 was familiar to experience for long ages before science gave 

 the explanation. Most of our iield fungi, large and small, 

 are saprophvtes and of great economic importance in break- 

 ing up organic remains which otherwise would hopelessly 

 encumber the ground. 



Parasitism. Parasites and saprophytes are intimately 

 related. Certain fungi are constantly parasitic, they are 

 obligate parasites, while others are facultative parasites, 

 being able to pass from one condition to the other. There 

 is no apparent distinction between the hyph^e of the different 

 tvpes : in all there are branching septate filaments, and, as 

 Zellner* has pointed out, there are no principal differences 

 betw^een their cell contents, though as parasitic hyph^e are 

 in direct contact with living protoplasm, the substances 

 thev excrete mav be toxic and give rise to pathological 

 phenomena. 



Interesting experiments have been made on the origin 

 of parasitism, which tend to prove that it is an acc{uired 

 habit. Ravf found, for instance, that after prolonged culture 

 on nutritive media, Lstilago Maydis, underwent certain 

 changes that lessened its power of attacking the living host 

 plant : it reverted to the saprophytic condition. Massee:|: 

 studied the matter from the standpoint of the host, and he 

 demonstrated that there is some substance in the cells of the 

 host that is attractive to its particular fungal parasite " in 

 other words, infection is due to positive chemotaxis." By 

 injecting a substance chemotactic to a saprophytic fungus 

 into the cells of the host, he could induce the saprophyte to 

 become parasitic. It has also been observed that certain 

 fungi pass very easilv from the saprophvtic to the parasitic 

 stage even in natural surroundings. Massee§ quotes an 

 instance observed by him in CJadosporium epiphyllum, a 



* Zellner, 'lo. t Ray, '03. + Massee, '04. § Massee, '14. 



