CHAPTER 11. 

 EEACTION 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 diflerently 

 under attacks of the same fungus. 



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

 A. Killing of 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 they derive nutriment at the cost of the 

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

 grains, 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 



' Billroth ("liber die Einwirkungen lebender Pflanzen iind Thierzellen aufeinan- 

 i\er," Samm/un;/ Medic. Schri/ten. Wiener klin. Wochenb/atf, 1890), compares in a 

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

 tal)le tissues. He employs Virchovv'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 Lewin. 



- Perniciasmus. 



