Effect of Manganese Compounds 81 



of the Australian Coniferae. The authors conclude that manganese 

 may be essential to the growth of these plants, and that its association 

 with plant life may be considered to date back to past geological time, 

 as is indicated by plates illustrating fossil woods. 



II. Effect of Manganese on the Growth of Higher Plants. 



1. Toxic effect. 



(a) Toxic action of manganese compounds in the presence of soluble 

 nutrients. 



Little work seems to have been done on the action of manganese 

 compounds in water cultures. Knop (1884) just indicated that man- 

 ganese compounds had no effect on maize, but gave no details. Japanese 

 investigators touched on the matter in the course of their extensive 

 experiments with this element. Aso (1902) found that the greater con- 

 centrations of manganese sulphate exercised an injurious influence on 

 barley. Even in solutions with as little as "002 ^ manganese sulphate 

 (= 1/60,000 MnSOi) the roots gradually turned brown, the lower leaves 

 following suit. The brown colour was concentrated at certain points of 

 the leaves, and microscopical examination showed that the membranes 

 of the epidermal cells, and in some cases the nuclei, were stained deeply 

 brown. The greatest concentration endured by barley without injury 

 seemed to be about 01 per 1000 = 1/100,000. The presence of iron in 

 the food solutions seems to counteract the effect of the manganese to 

 some extent by delaying the yellowing of the leaves. Wheat proved very 

 similar to barley in its reactions, though more iron is necessary to give 

 good healthy growth. Aso states that wheat is able to overcome the 

 injurious action of manganese much more readily than is barley. With 

 peas the yellowing of the leaves was delayed, probably on account of a 

 sufiScient supply of iron in the reserve stores of the seeds. 



Loew and Sawa (1902) found that "25 % = 1/400 MnSO* (anhy- 

 drous) kills pea plants within five days and that the green colour is 

 gradually affected with more dilute solutions. Barley and soy beans 

 were grown in nutritive solutions with either iron sulphate or manganese 

 sulphate or both (-01 % FeSOi, "02 % MnSO,, -01 % FeSO^ + "02 % MnSO^). 

 At first the growth was increased by the action of two salts together, 

 but eventually the shoots turned yellowish, and assimilation was de- 

 pressed, so that decreased nutrition led to relaxation in the speed of 

 growth, indicating the toxic action due to the manganese sulphate. 



