DISEASES CAUSED BY FUNGI 6i 



hence we have no means of determining the nature or affinities 

 of the fungus, and as a consequence no infection of other rye plants 

 can take place, and the distributional area of the fungus will in 

 future be determined by the distribution of infected host-plants. 

 We have now existing two races of each of the three rye-grasses 

 mentioned above. One race infected, and always producing in- 



Base of a larch seedling attacked liy the fungus called 

 Arniillayia niellca. The bark is cut away to show the 

 white sheets of mycelium running up inside the bark. 



fected seed. A second race free from infection, and without the 

 possibility of becoming infected, Microscopic examination of 

 commercial samples of the seed of L. tcmulentum or darnel showed 

 that over 80 per cent contained the mycelium of the fungus, hence 

 the facility for a world-wide dispersion of diseased darnel, rye- grass , 

 and Italian rye-grass. 



A second proof that parasitism is an acquired habit is afforded 



