DISEASES OF PLANTS 



67 



good yield of ripe seeds. But although the vegetative parts of 

 the plant were free from symptoms of manganese deficiency, 

 33 per cent of the seeds were severely affected with marsh spot, 

 24 per cent were slightly affected, while 43 per cent were normal. 



The cultures supplied with 500/u,g. of manganese per litre grew 

 normally and vigorously and showed no symptoms of marsh spot. 



The necessity for manganese was also shown by the yield of 

 the cultures; Piper's results are given in Table IV. 



Table IV. Yield of peas in water cultures supplied with 

 different quantities of manganese. (Data from Piper) 



Cone, of 



Mn in 



^g. per 



litre 







5 



10 



20 



500 



Yield in g. per plant 



Shoots 



4-3 

 12-5 



18-2 

 21-9 

 30-7 



Roots 



1-3 

 4-0 

 3-7 

 3-2 

 3-5 



Seeds 











0-4 

 10-2 

 13-5 



Total 



5-6 

 16-5 

 22-3 

 35-3 



47-7 



No. of 



seeds 



per 



plant 





 

 6 



68 

 88 



Incidence 

 of marsh 



spot 

 per cent 



100 



57 







These results demonstrate very clearly that marsh spot arises 

 from a partial deficiency of manganese. 1 



Frenching of Tung Trees. Aleurites, a genus of the Euphor- 

 biaceae, contains five species which are of economic importance 

 on account of the oil yielded by their fruits. They are all trees 

 growing to a height of 25 to 40 ft. The species A. fordii, the 

 tung tree or tung-oil tree is the source of tung oil, a drying oil 

 used in the manufacture of paints, varnishes and linoleum and 

 for waterproofing. 



In plantations of tung trees in Florida, Reuther and Dickey 

 (1937) reported a rather widely distributed affection which they 

 described as 'frenching'. It is possible that this disease was 

 previously unnoticeo because it was masked by another, known 

 as bronzing, attributed to a deficiency of zinc and described 

 later. In trees affected with frenching, chlorotic areas develop 

 between the veins of the leaves, and as the disease advances the 

 tissue in the chlorotic areas dies and necrotic spots arise. 

 Premature abscission of leaves may follow. 



1 After this was written E. J. Hewitt (1945) described experiments 

 in which he succeeded in inducing symptoms of marsh spot in broad 

 beans ( Vicia Faba) and runner beans (Phaseolus multiflorus) grown in 

 manganese -deficient sand cultures. 



