BULLETIN 231] 



WALNUT CULTURE IN CALIFORNIA. 



339 



How 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 in- 

 terior of the tissue. These 

 stomata on the nuts are ar- 

 ranged in groups of from 

 five to a dozen or more, and 

 are to be found on the paler 

 green specks that spot the 

 surface of the husk of the 

 green nuts. It is through 

 these openings that the bac- 

 terial organism can gain 

 entrance to the interior of 

 the tissue of the young nuts. 



The blight organism is 

 motile and when carried to 

 the surface of the nut by 

 moisture, such as fogs and 

 heavy dews, can use this 

 moist surface to swim 

 directly into the stomata 

 or breathing pores just de- 

 scribed. When once in the 

 interior of the nut the con- 

 ditions are favorable for 

 further development. While 

 these stomata have the power 

 to open and close, they are 

 probably never so closely 

 shut that the small germs 

 could not enter. The moist 

 conditions favorable for the 

 entry of the germ or bac- 

 terium through the stoma 

 are also just the conditions 

 necessary for keeping this 

 entrance open. 



Two Seasons Compared. 

 The two years of 1907 and 

 1908 well illustrated the two 

 extremes of much and practically no bacteriosis of the walnut. The 

 year 1907 was very favorable for the development of this trouble, while 



FIG. 86. Surface of green walnut, showing two 

 groups of stomata through which the blight 

 germ enters. Much enlarged. Each group 

 represents one of the light-colored spots on 

 the surface of the green hull. 



