XL THE MULBERRY BLIGHT 



Type. This is a blight in many respects resembling fire 

 blight of the pear (No. XII) but slower in its action and with 

 a correspondingly greater tendency to spotting and distortion 

 of the leaves (Figs. 262, 263), in which it resembles the walnut 

 blight, and the leaf-spot of beans (No. VIII). Dark, sunken, 

 longitudinal stripes preceded and bordered by a translucent 

 area also appear on the young shoots. These sunken spots 

 often show a whitish or yellowish bacterial ooze, drying glossy. 

 If the surface is dry this ooze often exudes from the lenticels 

 in the form of cirri (Fig. 264). In such young shoots both 

 wood and bark are invaded by the bacteria, and the end of the 

 disease is either shriveling and death of the shoots (Figs. 265 to 

 267), or a curved one-sided growth. As in pear blight, we have 

 to do, primarily, with a bark disease (Figs. 268, 269). The 

 disease usually begins in the shoots of the season (F^g. 270), 

 but the blight frequently extends beyond these, especially into 

 shoots of the previous year. On the older parts the disease 

 occurs in the form of cankerous patches. As in fire-blight 

 of the pear, the tendency of the bacteria to ooze to the surface 

 is strong. 



On the leaves there are numerous coalescing and slowly 

 enlarging spots which are water-soaked in appearance at first, 

 then brown or black, the surrounding tissues becoming yellow. 

 The bacteria occupy the intercellular spaces and form cavities 

 (Figs. 271, 2725). On the midrib and veins dark sunken spots 

 appear, similar to those on the shoots. Leaves attacked early 

 in their development become variously distorted (see also No. 

 VIII). 



So far as known, mulberry trees are seldom or never killed 



,340 



