MODE OF LIFE OF THE PARASITIC FUNGI. 9 



I can however hardly regard as parasites, fungi like these 

 which live on an accidental outflow from plants or plant-cells, 

 even though they regularly frequent places where an outflow is 

 to be expected. They exert no influence on the host-plant, 

 and they are nourished by substances which can no longer be 

 regarded as belonging to the host. I would rather include 

 them amongst non-parasitic epiphytes .which, without specially 

 adapting themselves, settle on any part of a living plant where 

 sugary solutions suitable for their nutriment may occur. One 

 might imagine however such epiphytes inducing a diffusion of 

 nutritive substance from the cells of the host-epidermis to the 

 closely adherent fungal hyphae ; then we should have the 

 simplest mode of parasitic acquisition of nutriment on the part 

 of epiphytes. They would take up food-material from the epi- 

 dermal cells in much the same manner as many intercellular 

 hyphae do from the adjoining walls of the host-cell.^ 



Epiphytic parasites frequenting the surface of plant-organs 

 generally endeavour to increase their supply of nutriment from 

 the host-cells by formation of haustoria, which pierce the cuticle 

 or the whole cell-wall. Blisgen has shown experimentally 

 that the adhesive discs, often formed on the germination of a 

 spore, owe their origin to a contact-stimulus; the formation and 

 direction of the infecting hyphae, on the other hand, though 

 depending on this, are much more determined by a stimulus 

 originating from the host-cell itself. In this we have a confirma- 

 tion of the accuracy of our definition of 

 parasite and saprophyte. 



The appressoria, adhesion-organs or 

 adhesive discs just mentioned, are char- 

 acteristic of many parasites. They are 

 formed chiefly on epiphytic mycelia, 

 but also accompany the earlier life of 

 other fungi. In the case of epiphytes, 

 pores are formed on definite places of 



, 11 . 1. n y. J, ^'O- 1-— SP. Spore of Erpsipheae 



such an adheSlVe-dlSC, and irom these umbelliferarum germinating on the 



, . Ill 11- epidermis of a host-plant; an ad- 



haUStoria are developed, or a hypha is hesion-discandhaustorlumhavebeen 



ff J w- 4.1- I. .. 1 4. 4- *'"™"*- CAfter l)e Bary.) 



given on and enters the host-plant to 



form a mycelium. The appressoria of the Erysipheae are very 



characteristic ; in many they are broad lobed discs (Fig. 1) ; in 



^ Compare those cases of parasites on insects and fungi already given, p. S (note). 



