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. 1 

 A. KILLING OF Hosi'-CELLS. 2 



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. 

 Tin- most primitive of all are numerous species which, applying 

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

 the cavity. There they derive nutriment at the cost of the 

 living cell-content, the plasma, cell-sap, chloroplasts, starch 

 -rains, etc., and finally kill the cell. The host-cell does 

 not survive the later development and reproduction of the 

 parasite. The effect of the fungus is however limited to the 



1 liilliutli ("iilif-r die Kimvirkungen lebender Pflanzen und Thierzellen aufeinan- 

 d.-r," XitinniliiiKj Medic. Schrifti'ii. Wiener klin. Wochenblatt, 1890), compares in a 

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

 tiilile tissues. He employs Virchow's terms " formative stimulus '' and " formative 

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

 i.ut un>\\ i li.-, of definite form or the formation of new tissues; the latter, the 

 capacity <>t the tissues to react to such stimuli, and to produce outgrowths, 

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

 >f animals and plants recently formed the subject of a short paper by Lewin. 



- Perniciasmus. 



