EFFECT OF PARASITIC FUNGI ON THEIR HOST. 21 



by pustules of Urocystis violae, the mycelium of which had 

 perennated in the stem. Kerner in his '' Pflanzen-leben " ^ 

 mentions a similar case where flowers of Primula clusiana and 

 P. minima attacked by Uromyces primulae integrifoliae unfolded 

 prematurely in autumn. 



E. Preservation op the Host-Plant and of Host-Tissues. 

 (Conservation.) 



In contrast to those parasites which attack a plant, or parts of 

 it, and immediately kill it or otherwise exert a direct destructive 

 influence, we have these which live for a longer or shorter period 

 with their host without producing such an effect. Cohabitation 

 of this kind may last only for a short time and terminate with 

 the first reproductive period of the fungus, or it may last for 

 years as a perennating symbiosis, or as a perpetual one like that 

 of lichens. 



This phenomenon is particularly conspicuous amongst the 

 Uredineae. These throughout their whole development adapt 

 themselves to an existence with living host-cells, so that the 

 latter die only after the reproduction of the fungus. Frequently 

 the mycelium lives in perennial organs for a length of time, 

 even for many years. The attacked parts are of course injured 

 to a certain extent, and hypertrophy of the most varied kind, 

 accompanied by characteristic phenomena, may take place, yet 

 this only towards the termination of the period of development. 



The Ustilagineae are in a similar manner adapted to an exis- 

 tence in living organs, and there produce their spores. At the 

 time of spore-formation and liberation thfey are deadly enemies of 

 their host-tissues, yet previous to this they vegetate in the 

 living tissues with little or no apparent injurious efiect. Some 

 like Ustilago perennans, even pass the winter in the living host- 

 tissue without killing it. 



The individual species of the Hysteriaceae, Discomycetes, 

 Pyrenomycetes, Hymenomycetes, and lower fungi differ very 

 much in their action ; many of them inhabit living tissues for a 

 length of time without injurious effect, while not a few, like the 

 Exoasceae, even perennate from year to year. The galls pro- 

 duced as a result of Exohaddium do not die till the fungus has 

 reproduced itself. It is unnecessary at this place to give details 



^ English Edition, Natural History of Plants (Oliver), ii. , p. 525. 



