92 TRACE ELEMENT DEFICIENCY 



Australia, from Smith and Thomas (1928) in regard to plum, 

 apple, pear and olive in California and from Pittman (1936) for 

 Citrus, plum and apple in Western Australia. 



Oserkowsky and Thomas (1933) showed that the condition of 

 the leaves of Bartlett pear trees in relation to this disease corre- 

 sponded to their copper content. Thus, leaves affected with 

 exanthema contained 3-1-5-1 p. p.m. of the dry weight, while 

 normal leaves from localities free from the disease contained 

 11-20 p. p.m. of the dry weight. While these workers considered 

 that these analyses afforded strong evidence that exanthema 

 resulted from a deficiency of copper, they pointed out that there 

 was no evidence to decide whether the disease was due directly 

 to copper deficiency or whether the effect was an indirect one 

 such as might be brought about, for example, if the action of 

 copper resulted from its neutralizing the effect of toxins absorbed 

 by the plant from the soil. 



More definite evidence that exanthema in Citrus is due to a 

 deficiency of copper was provided by a culture experiment 

 described by Haas and Quayle (1935). Valencia orange trees 

 grafted on sour-orange stocks were grown in twelve large tanks 

 containing pure sand. A nutrient solution containing all the 

 known mineral nutrients except copper was supplied to the 

 trees. Although for some years the trees grew vigorously, after 

 seven years they displayed typical and pronounced symptoms 

 of exanthema including the S-shaped growing shoots, exudation 

 of gum, blisters on the surface of the shoot and dying back of 

 many shoots. The leaves became covered on the ventral side by 

 a resinous stain and many leaves developed chlorosis. 



The effect of copper deficiency on deciduous fruit trees in 

 South Africa has been described by Anderssen (1932). Apple, 

 pear, plum, peach and apricot trees are all affected to different 

 degrees. Thus plums, peaches and apricots exhibit a very 

 decided chlorosis in the areas of the leaves between the veins. 

 This is accompanied by very marked rosetting of the leaves, 

 cessation of apical growth followed by the dying back of the 

 branches from their apices. Apples, on the other hand, exhibit 

 chlorosis much less frequently, but rosetting is severe and the 

 long shoots die back. Pears similarly do not show chlorosis very 

 often, but unlike apples they do not develop rosetting; however, 



