10 March, 1916.] 



The Walnut. 



159 



of disease that may develop, as luiuiid conditions are especially favorable 

 for its spread. It has been proved again and again by experiments that 

 infection is produced when water containing the disease germs is sprayed 

 on the surface of the young nuts, while the untreated ones are free from 

 the disease. Then, for infection to take place under natural conditions, 

 it only becomes necessary for virulent germs to come in contact with 

 immature nuts, and water is apparently the principal agent in conveyinc: 

 the germs from the diseased lesions to the young growth or small nuts 

 below. Rains or fogs occurring in the spring, after the nuts appear, 

 particularly at night, are very favorable for the dissemination and new 

 infection of the small nuts. During those conditions the trees become 

 saturated, water dripping from one portion of the tree to another, which 

 could easily carry the disease organisms to healthy tissue. 



Fig. 34. — Section of surface of green walnut, showing a group of stomata 

 through which the blight germs enter. Much enlarged. (After Smith, 

 BiUletin 231.) 



Ilow the Germ Enters the Tissue. — Nuts, as well as the leaves and 

 young shoots, are provided with stomata, or breathing pores, through the 

 epidermis into the interior of the tissue. These stomata on the nuts 

 are arranged in groups of from five to a dozen or more, and are to be 

 found on tlie paler green specks that spot the surface of the husk of the 

 green nuts. It is through these openings that the bacterial organism 

 can gain entrance to the interior of the tissue of the young nuts. The 

 blight organism being motile and when carried to the surface of the 

 nut by moisture, such as fogs, heavy dew, and rain, can use this moist 

 surface to swim directly into the stomata, or breathing pores, just 

 described. When once in the interior of the nut, the conditions are 



