84 PRESIDENTIAL ADDRESS SECTION C. 



to the present the fire Wight is not known to occur in this 

 country. 



Crown Gall. Bacterium timicfaciens Smith and Towns. 



Dr. Pole Evans has shown that the crown gall occurring in 

 South Africa is caused by the same organism {B. tumefaciens) 

 as the American gall. Crown gall is a common nursery trouble 

 throughout the country, and sometimes becomes severe in the 

 orchard after hail injury. Willow trees are particularly subject 

 to crown gall, and seem to act as reservoirs of infection for 

 fruit trees in their vicinity. 



Mulberry Blight. Bacterium mori. (Boy and Lamb.) 



Sim (15). 



Mulberry blight is of very common occurrence, but does 

 not cause serious injury except to the Black mulberry, Morus 

 nigra. It causes spotting and distortion of the leaves, discolora- 

 tion and necrosis of the shoots, and a general dwarfing of the 

 whole tree. 



Walnut Blight. Bacterium juglandis. Pierce (21). 



The Calif ornian walnut blight is very prevalent in Natal, 

 both in the nursery and the orchard, and many fine trees have 

 been destroyed, as year after year they failed to produce a crop. 

 It also occurs in the Eastern Province of the Cape, the Orange 

 Free State and the Transvaal, and causes serious trouble when 

 there is abundant rain and cloud in the early summer. The 

 leaves and twigs are attacked, but the most serious consequence 

 IS the wholesale destruction of the young nuts, which become 

 badly spotted and fall prematurely. 



Mango Blight. Bacillus mangifercv Doidge (14). 



The mango blight seriously affected the export of mangoes 

 from the Barberton district, and the disease is also severe in 

 Natal, and occurs in the Pretoria and Rustenburg districts of the 

 Transvaal. Discoloured blotches appear on the leaves and fruit, 

 and not only are the mangoes disfigured, but when they are 

 attacked early, fall to the ground in great numbers when the 

 fruit is only half grown. 



Coconut Bud Rot. Bacillus coli. (Esch) Mig. 



Coconut bud rot occurs in Portuguese East Africa, and it 

 has been shown by Dr. Pole Evans that the causal organism is 

 Bacillus coli^ and the disease is identical with that which occurs 

 in other tropical countries. 



Angular Leaf Spot of Cotton. B-acteriiim malvacearum Sni. 



As the name indicates, the bacterial disease of cotton is 

 characterised by the formation of dark, angular spots on the 

 leaves and bolls. It seems to occur wherever cotton is culti- 



