Baker and Smith (1910) paid special attention to manganese in their exhaustive work on the Pines of Australia. They state that “in the anatomical investigations of the timber, bark, and leaves of the various species, there was found to be present, in a more or less degree, a naturally brownish-bronze coloured substance, which invariably stained dark brown or almost black with haematoxylin.” This substance on careful investigation proved to be a compound of manganese. The quantity present varies with the species and also with the plant organs. The different species of the genus Callitris show variable percentages of manganese from a maximum of 0·230% in _C. gracilis_, to a minimum of 0·010% in _C. robusta_. The percentage of manganese in Australian Coniferae other than Callitris is given by the authors in the following table: Ash of timber of Agathis robusta 0·145% Mn. „ „ Araucaria Cunninghamii 0·054% „ „ „ Araucaria Bidwilli 0·077% „ „ „ Actinostrobus pyramidalis 0·077% „ „ „ Podocarpus elata 0·002% „ „ „ Dacrydium Franklini 0·129% „ „ „ Athrotaxis selaginoides 0·019% „ „ „ Phyllocladus rhomboidalis 0·145% „ Air-dried black gum of Agathis robusta 0·0046% „ „ „ Araucaria Cunninghamii 0·0038% „ Baker and Smith assume that manganese is essential to the production of the most complete growth of Coniferae. The element is found in these plants even when they grow on soils containing only traces of manganese and it is suggested that possibly the excess or deficiency of manganese in the soil helps to govern the location of certain 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._