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UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



Young trees are much more free from bacteriosis than are those that 

 have been in bearing for a longer time. 



It should be remembered that other causes than bacteriosis may make 

 the small nuts fall, as for instance poor pollination, which may result 

 from a lack of pollen or unfavorable climatic conditions, the small nuts 

 being very susceptible to cold at this time. In the English walnut the 

 catkins and nuts are produced in the spring in separate clusters on the 

 same tree. (See Fig. 1.) The catkins are the male flowers and bear 

 the pollen. They are always found on the old wood, and these may be 

 seen as rather long buds in the late autumn. The small nuts are found 

 on the new growth. These two kinds of flowers should appear at about 



FIG. 82. Half-grown walnuts affected with Bacteriosis. 



the same time, but on the seedling trees there is the greatest variation. 

 A tree may have a very limited number of catkins or may be abundantly 

 provided. These may appear at the same time as the nuts, or too early 

 or late to be of much service in fertilizing them. 



Blossom End Infection. While the nuts may be infected at any 

 point in the surface, by far the most common as well as most virulent 

 form of infection is at the blossom end near what is technically called 

 the stigma. This is the weakest part of the nut and is especially sensitive 

 to the blight. The bacteriosis is very bad on the small nuts, and when 

 once it has started at this point it rapidly continues its growth within 

 the tissue, until the small nut is sufficiently weakened to fall. Not all 



