2 THE PARASITIC FUNGI. 



§ 1. DEFINITION OF THE PARASITISM OF FUNGI. 



Paragitin IP^^gi are those whie li,— stkfttbktod bjL- the cell 



cqnteiits,-iai-aB£Ab.er living, plant, penetrate wholly or partiaU. 



inte„itS tigRiiPS, anH rlraw t.hp.ir Tiiit.rinTpnt, fnHltt.Jihat».SOUiec. 



Sa prophytic Fungi _.-are iJios.e_ which__ make- no attempt -to 

 penetrate the tissues of living plants, but derive their nutriment 

 from a dead substratum. 



Intermediate between these two extremes come those fungi 

 which, in consequence of some stimulus, attempt to effect an 

 entrance into the tissues of living plants by the secretion of some 

 fluid or ferment, but only attain their object after first killing the 

 part they attack (e.g. Sclerotinia sclerotiorum). A special position 

 must also be ascribed to certain forms which inhabit the wood 

 of trees, but have not the power to penetrate through the outer 

 tissues; they depend on first gaining entrance through wounds 

 into dead parts of the bark or wood, and, after living there for 

 a time as saprophytes, extend into the living elements and cause 

 their death. 



Many parasites may be artificially cultivated so as to pass 

 some part of their life-history on dead pabulum, and even in 

 natural conditions many of them regularly live for a season in 

 a saprophytic manner. On this account it appears to me more 

 correct, in distinguishing between parasites and saprophytes, to 

 lay less weight on the adaptation to nutrition and more on their 

 response to the stimuli exerted by living plant-cells. The nature 

 of this stimulus which affects parasitic hyphae has not as yet 

 been investigated. It appears probable, however, especially from 

 the investigations of Pfeffer and Miyoshi,^ that the influence is 

 primarily a chemical one, and that the nutritive value of the 

 stimulating substance is not a measure of the ensuing effect. 

 Biisgen states that the formation of adhesive-discs by germinating 

 spores is induced by a stimulus due to contact, whereas the 

 production and penetration of the first haustorium is independent 

 of contact, and is probably due to some chemical stimulus (see 

 p. 9). Miyoshi's investigations have also proved that saprophytic 

 fungi are capable of penetrating into living plant-organs, even 



'Miyoshl. " Ueber Chemotropisraus d. Pilze. " Botan. Zeitung,lS9i; also "Die 

 Durchbohrung von Membrauen durch Pilzfatlen." Pringsheim's Jahrhuch, 1895 



PfefiFer. "Ueber Election organischer Nahrstoffe." Pringnhtim's Jahrhich, 

 1895. 



