218 TEXT-BOOK OF FUNGI 



the host-plant, finally again entering the seed, where it 

 remains in a resting condition until the ' seed ' commences 

 to germinate, when the same cycle is repeated. A series 

 of experiments proved that infected plants were more 

 vigorous than uninfected ones. So certain is the fungus 

 of perpetuating itself by this vegetative method, without 

 ever quitting the host-plant, that the production of spores 

 has been completely arrested, hence there are no means of 

 ascertaining with certainty the affinities of the fungus. 



In the absence of spores no other plants of the same 

 kind can be infected, consequently there exist two races of 

 each of the three kinds of rye-grass, one race infected with 

 a fungus, the other race uninfected, and without a possi- 

 bility of becoming infected. Microscopical examination 

 of a commercial sample of darnel * seed ' showed over 

 eighty per cent, to be infected. 



Many other instances could be enumerated where disease 

 is perpetuated from generation to generation by means of 

 perennial mycelium, but perhaps sufficient has been written 

 to show that this method of disease perpetuation and dis- 

 tribution is a factor not to be ignored, and that it probably 

 plays a much more prominent part in these directions than 

 is generally supposed. 



LEGISLATION, AND THE SPREAD OF PLANT 

 DISEASES CAUSED BY FUNGI 



It is well within the mark to state that the annual loss 

 throughout the world, due to injury caused to cultivated 

 plants by parasitic fungi, exceeds ^150,000,000 sterling. 

 Probably double this amount would be nearer the truth. 



