80 TRACE ELEMENT DEFICIENCY 



necrotic areas which increase in size and merge with one 

 another until the whole leaf is dead. Meanwhile the younger 

 chlorotic leaves continue to unroll and as they expand develop 

 typical yellow intervenal striping. Internodes fail to develop 

 properly so that the whole plant is stunted. The root system, 

 however, appears to be normal. 



The effect of various fertilizer treatments on maize plants 

 affected with white bud was examined by Barnette and Warner. 

 They found that a dressing which included 20 lb. of zinc sulphate 

 per acre induced a very much higher yield of grain than any 

 inorganic dressing which did not include zinc. With the applica- 

 tion of zinc sulphate the chlorotic plants recovered a normal 

 green colour, made healthy growth and produced grain. The same 

 effect was produced by the application of stable manure or leaf 

 mould, while chicken manure and alkaline peat produced some 

 improvement in the condition of affected plants. Spectroscopic 

 examination of the ash of these various organic manures 

 revealed the presence of zinc in all of them. The work of Barnette 

 and Warner, although not definitely establishing white bud of 

 maize as a disease due to deficiency of zinc, indicates the prob- 

 ability of this being the case. 



The possible relationship of bacteria to white bud has already 

 been mentioned in the discussion of little leaf of deciduous fruit 

 trees (p. 75). 



3. Diseases Attributable to a 

 Deficiency of Boron 



The effects of boron deficiency in plants have been well dealt 

 with by Brenchley and Warington (1927) and more recently by 

 R. W. G. and A. C. Dennis (1937, 1939, 1941, 1942). From the 

 accounts of these and other authors it appears that the first 

 external symptom of boron deficiency is generally the death of 

 the apical growing point of the main stem. This is followed by 

 growth of lateral buds into side shoots, the apices of which 

 then die. Further symptoms are slight thickening of the leaves, 

 a tendency for these to curl, and sometimes a slight chlorosis. 

 The petioles, and even the leaves, often become brittle, flowers 

 may not form, or if they do fruit may not set. Stunted root 

 growth is general. 



