DISEASES OF PLANTS 95 



cereals in South Australia and also found that it could be con- 

 trolled by the application of copper sulphate to the soil. 



Oats were grown by Brandenberg (1933, 1934) in water 

 culture in which the amount of copper present in the culture 

 solution was carefully controlled. When copper was excluded, 

 growth was poor and the plants developed the symptoms of 

 reclamation disease. With small amounts of copper added to 

 the solution vegetative growth was more normal, but fruiting 

 was not unless the concentration of copper in the solution was 

 at least 0-5 mg. per litre. More recently, Piper (1942) has carried 

 out water-culture experiments with specially purified reagents 

 in which the initial copper concentration of the culture solutions 

 varied from to 3 mg. per litre. In addition to the ordinary 

 major mineral nutrients the solutions contained small quantities 

 of boron, zinc, manganese and molybdenum as well as sodium 

 chloride. The main results were as follows. In the cultures 

 without copper, 27 days after setting the seeds to germinate, 

 growth and tillering were noticeably less than in cultures pro- 

 vided with copper. During the next fortnight these symptoms 

 became more pronounced, the leaves were a paler green, the tips 

 of the younger leaves appearing definitely chlorotic, withering 

 and dying without unrolling, while the base of the leaf con- 

 tinued to emerge and grow. In subsequently emerging leaves 

 these symptoms were more pronounced until growth of the 

 tiller ceased and its death ensued. 



In cultures provided with 3/tzg. of copper per litre definite 

 symptoms of copper deficiency were not observed until 7 1 days 

 after setting the seeds to germinate, although the plants made 

 less growth than tho&e with more copper. Slightly older leaves 

 developed a marginal chlorosis. Ultimately the main tillers 

 ceased growth and died, and although secondary tillers were 

 produced these also developed the symptoms already described 

 and ultimately stopped growing. 



When cultures were initially provided with 6^g. of copper per 

 litre more growth took place before the symptoms of deficiency 

 developed in the youngest leaves. In these cultures the slightly 

 older leaves exhibited a loss of turgor so that they appeared limp 

 and drooping. Secondary tillers developed as before, but all 

 stopped growing before ear production. 



The plants in a culture solution containing initially 10/i,g. of 



