BULLETIN 231] WALNUT CULTURE IN CALIFORNIA. 325 



The work here recorded covers the results of previous investigators, 

 verifying them in most cases, while some new data has also been added. 



Cause of Disease. The disease thus far discussed has been con- 

 clusively proven to be produced by a species of bacteria growing in 

 the diseased parts, and hence is very properly referred to as Bacteriosis. 

 A microscopic examination of diseased tissue shows countless numbers of 

 these small, rod-shaped organisms to be present. By employing 

 bacteriological methods pure cultures of these germs were obtained and 

 then these pure cultures were used in making artificial inoculations into 

 healthy nuts and shoots, thus again producing the typical disease. The 

 organism has been isolated many times, and no difficulty has been 

 experienced in always producing the disease by inoculation from culture 

 if the tissue was in an active growing condition. 



The walnut blight organism belongs to what are called the bacteria; 

 low forms of plant life that are ^extremely small in size and increase 

 rapidly in number by elongation and division or fission. When grown 

 in artificial cultures in mass they have a shiny yellow appearance. 



Confusion with Marsonia juglandis. It is important to refer to this 

 trouble in some detail for it has been confused with our walnut bac- 

 teriosis and bears a close resemblance to it in very many respects. This 

 disease is caused by a fungus that is not uncommon in the Eastern 

 States on the leaves of the butternut, Juglans cinerea, and on the leaves 

 of the black walnut, Juglans nigra. So far as our observations have 

 gone the trouble does not affect the nuts or branches of these trees. In 

 France the fungus occurs on the nuts of the English walnut as well as 

 on the branches, causing them to have a black appearance, like our 

 Bacteriosis. This disease is described* by Prillieux and Delacroix of 

 the Institute National Agronomique and Laboratoires de Pathologic 

 Vegetale. No mention in this article or any other scientific literature is 

 made of our Bacteriosis occurring in France. 



In California no species of Marsonia is known to occur on English 

 walnuts. There is a species of Marsonia recorded by A. D. McClatchief 

 as occurring on the leaves of Juglans calif ornica, but this trouble is not 

 at all common. In the spring of 1910 a species of Gloeosporium was 

 found attacking the leaves of Juglans calif ornica. This occurred only 

 on the leaves and could not be confused with the Marsonia referred to 

 in the following paragraph : 



The following is an abstract from the article by Prillieux and Dela- 

 croix: Marsonia juglandis (anthracnose) is parasitic on leaves, young 

 shoots and fruits of the Juglans regia. The disease forms round spots 



*Maladies des Plantes. Les Maladies des Noyers en France. 

 t Seedless Plants of Southern California, p. 378. 



