82 Effect of Manganese Compounds 



The Rothamsted experiments supported Aso's work on the action of 

 manganese sulphate on barley, concentrations of the salt above 1/100,000 

 having a retarding influence on the growth, the roots being coloured 

 brown and the leaves also showing discolouration. At an early stage in 

 growth the lower leaves of the plants receiving the most poison began to 

 be flecked with brown spots, which were at first attributed to an attack 

 of rust. Suspicion was soon aroused, however, and a closer microscopic 

 investigation showed that no disease was present, but that the cells in the 

 affected spots were dead and brown, though they retained their shape. 

 The dead cells at first occurred in small patches, which spread and 

 coalesced until ultimately the whole leaf was involved. Some of the 

 affected leaves were detached and fused with a mixture of sodium car- 

 bonate and potassium nitrate. On dissolving up the resulting mass with 

 water a green colouration was obtained, indicating the presence of man- 

 ganese in the leaves. This shows that the manganese is taken up by 

 the roots, transferred to the leaves and then deposited in them, the lower 

 leaves being the first affected. 



The presence of manganese in the nutritive solution retarded the 

 ripening of the grain to some extent, as when the grains from the control 

 plants were hard and ripe, those from plants treated with 1/10,000 MnS0 4 

 were green, those with 1/100,000 were a mixture of ripe, half-ripe, and 

 green grains, while plants which had received 1/1,000,000 MnS0 4 pos- 

 sessed ripe grains. 



Peas give similar results to barley so far as the vegetative growth is 

 concerned, the same retardation with the higher concentrations being 

 observed, while the brown discoloured patches in the lower leaves are 

 much in evidence. All traces of manganese in the leaves disappear when 

 the concentration falls to 1/250,000. On the whole peas are more sen- 

 sitive to manganese poisoning than is barley, and the higher strengths 

 of manganese prove more deleterious to them. 



(6) Toxic action of manganese compounds in sand cultures. 



Little work has been done on this aspect of the problem. Prince de 

 Salm Horstmar (1851) grew oats in sand with various combinations of 

 nitrogenous substances and inorganic mineral salts. He stated that 

 until the time of fruit formation manganese does not seem to be essential 

 to the oat unless iron is in excess in the substratum. 



(c) Toxic action of manganese compounds in soil cultures. 



A large body of work has been done with manganese in soil cul- 

 tures, but the toxic effect is hardly indicated, possibly because it is 



