78 TRACE ELEMENT DEFICIENCY 



normally, resulting in a bunched appearance of the foliage, the 

 twigs remain thin and adventitious buds sprout on the older 

 wood. Although the affection may be at first local, finally the 

 whole of the tree may be involved. Affected trees are unduly 

 subject to injury by the low temperatures of winter, and a 

 bronzed tree may come into activity in the following spring 

 smaller in size. By the third season after the first appearance 

 of bronzing a tree may be reduced greatly in size and, with its 

 almost bare branches, appear half dead. 



Mowry and Camp (1934) found that bronzing could be cured 

 by the application of about 1/4-1/2 lb. of zinc sulphate per tree 

 to the soil or by spraying the foliage with a spray containing 

 6 lb. of hydra ted lime and 3 lb. of 89 per cent zinc sulphate in 

 50 gal. of water containing some calcium caseinate spreader. 

 While not definitely committing themselves to the view that 

 bronzing of tung trees is a deficiency disease they conclude that 

 it should be considered the result of zinc deficiency until proved 

 otherwise. As a result of this work by Mowry and Camp on the 

 control of bronzing by the application of zinc sulphate Reuther 

 and Dickey were able to report in 1937 that comparatively little 

 bronzing was then to be found in properly conducted tung 

 plantations. 



Pinus radiata Rosette. Trees of Pinus radiata growing in 

 plantations on poor soil in Western Australia are liable to 

 exhibit a condition of rosetting reminiscent of that occurring on 

 so many species of trees in America already described. Field 

 trials of the effect of spraying with zinc chloride or zinc sulphate 

 described by Kessell and Stoate (1936, 1938) showed that, as 

 with other species affected by rosetting, treatment with zinc 

 was a cure for the disease. The presumption that rosette of 

 P. radiata is brought about by a deficiency of zinc was shown 

 to be correct by carefully controlled water cultures carried out 

 by Smith and Bayliss (1942). Removal of zinc, copper and lead 

 from the stock solutions was effected by the use of dithio- 

 carbazone. Boron, manganese and copper were added to 

 the culture solutions containing the usual major nutrients. 

 Zinc was added to the controls only. The method of purifying 

 the solutions did not remove molybdenum and it was not 

 necessary to add it. 



