376 Fruit-growing in Arid Regions 



The work of Arthur at the New York Agricultural Experiment 

 Station, in 1884 and 1885, should settle this point forever. Dr. 

 Arthur made cultures of blight germs in a liquid medium, which 

 were taken from blighted trees. These were pure cultures and 

 were carried through a number of generations. Blight was pro- 

 duced in trees by inoculating with the last culture. But to 

 satisfy those who might still say that the injury was due to the 

 liquid and not to the germs, inoculations were made with the 

 liquid from which the germs had been removed. This was ac- 

 complished by filtering through earthenware cells. The filtered 

 liquid was found to be entirely free from germs, and all inocula- 

 tions with it failed entirely to produce results. 



These experiments, which have been duplicated by many ex- 

 perimenters, prove beyond any possible doubt that this specific 

 micro-organism is the cause of blight. The germs, which are a 

 low form of vegetable life, feed on the cambium layer of the 

 plant. They gain entrance only through wounds in the bark or 

 through very tender tissue, such as is found in the nectaries of 

 flowers and possibly through the small openings which are abun- 

 dant in leaves and in the green bark of young twigs. 



Where do these germs originate? is often asked. Because they 

 are too small to be seen with the unaided eye this is difficult to 

 understand. They should be regarded simply as microscopic 

 weeds which live within trees instead of in the soil. We cannot 

 always satisfactorily explain where weeds come from, yet they are 

 always with us. Waite, of the Department of Agriculture, has 

 demonstrated that the germs must be distributed by mechanical 

 means, and that insects are very important agents in spreading 

 the disease. He found the germs developing in the nectar in the 

 blossoms and also found them adhering to the mouth parts of 

 honey bees after they had visited infected flowers. Thus it will 

 be seen that after one blossom has been infected, the disease is 

 spread rapidly, as numerous insects of various kinds visit flower 

 after flower. This accounts for the blighting of bearing trees, 

 while those which for some reason failed to bloom may be entirely 

 free. 



But the more important point in the life history of these germs 



