CHAPTER II. 

 REACTION OF HOST TO PARASITIC ATTACK. 



The reaction of the host to the attacks of parasitic fungi is 

 fairly constant for the same host and fungus. The various 

 fungi, however, exert on the same host-plant each an influence 

 of its own, while different host-plants behave very differently 

 under attacks of the same fungus. 



§ 4. EFFECT OF PARASITIC FUNGI ON THEIR HOST.' 

 A. Killing op Host-Cells.^ 



1. Absorption of living cell-content by parasitic fungi. 



The lower fungi give us examples of the simplest mode in 

 which fungus-parasites draw nutriment from their host-cells ; 

 particularly those forms parasitic on algae or other fungi. 

 The most primitive of all are numerous species which, applying 

 themselves to a host-cell, bore through its walls and enter 

 the cavity. There Jh^ey derive n utriment at the cost of th e 

 livin g cell-content, — the plasma, cell-sap, chloroplastSj__starch 

 grainSj__etc.. — and finall y^ kill~llie cel l. The hosf^cell does 

 not__SUX^ziKe — th£_ later development and reprod ii'^tin n nf the 

 parasite. The effect of the fungu s is however limi ted to the 



^ Billroth ("liber die Einwirkungen lebender Pflanzen vind Thierzellen aufeinan- 

 der," Sammlung Medic. Schri/ten. Wiener Idin. Wochenhlatt, 1890), compares in a 

 masterly way the effects of micro-organisms and of injuries on animal and vege- 

 table tissues. He employs Virohow's terms " formative stimulus"and "formative 

 irritability " ; the former to denote the capacity of micro-organisms in producing 

 outgrowths of definite form or the formation of new tissues ; the latter, the 

 capacity of the tissues to react to such stimuli, and to produce outgrowths, 

 etc. A comparison of the external phenomena of fungoid diseases in the case 

 of animals and plants recently formed the subject of a short paper by Lewiu. 



^ Perniciasmus. 



