OCCURRENCE OF MANGANESE IN SOIL AND ITS EFFECT ON GRASS. 359 



noted in the case of the Hawaiian soils. W. P. Kelley 

 (Zoc. cit.) reports that the first crop of pines showed but 

 little yellow colour during the first twelve months when 

 grown on the black soils. Later, however, the plants 

 became yellow and refused to grow. The soil itself also 

 appears to become darker in colour with the continued 

 growth of the pines. He concludes from this that there is 

 possibly some change brought about in the soil by the crop 

 itself, resulting in a change in the state of oxidation of the 

 manganese. 



Speaking generally concerning what is known of the action 

 of manganese in the soil, it may be regarded as proved 

 that in small quantities it is beneficial to some crops, that 

 in larger quantities it acts as a plant-poison, but whether 

 this is due to the direct action of the manganese itself or 

 to some secondary action on the soil-constituents is not 

 established. A quantity of manganese which is toxic to 

 some plants may be harmless towards others. Thus Aso 

 (loc. cit.) finds that barley and oats are not affected by 

 doses of manganese which are injurious to rice, and Kelley 

 states that the soils which do not grow pineapples give good 

 crops of sugar cane. The toxic action is greatest in winter, 

 and if the quantity of manganese present is not excessive 

 the affected plants often recover with the warm weather. 

 The compounds in which manganese plays the part of an 

 electro-negative element are the most toxic, and it appears 

 that some process goes on by which the manganese is 

 converted in the soil from an originally innocuous com- 

 pound to a more poisonous one, so that its presence is not 

 noticed in the soils for the first year or two. This process 

 is probably one of oxidation, as the higher oxides are found 

 to be more toxic than the lower. 



Corroboration of these results has been afforded by the 

 examination of patches of land at Milton (South Coast) in 



