CAN LITHIA BE A CONSTITUENT OF 

 PLANT-FOOD? 



Bv Professor Paul Damkl Haiin, M.A., Ph.D. 



Since the introduction of water-cultures into biochemical 

 research, it has been ascertained that the number of elements, 

 which are absolutely indispensable constituents of plant-food, is 

 rather small — potassium, calcium, magnesium, iron, sulphur, 

 pho.sphoms, carbon, nitrogen, oxygen, and hydrogen. In addi- 

 tion to these, a large number of elements have been observed in 

 different plants, of which some are of frequent or, rather, of 

 regular occurrence in the ashes of all land plants and in all 

 parts of the same plant — copper,* zinc,t manganese,! aluminium, 

 lithium. Midium, rubidium, caesium, barium, strontium, lead, 

 nickel, cobalt, silicon, chlorine, sodine, bromine, and fluorine. 

 Of this series of elements, three— chlorine, sodium, and silicon- 

 have been found in the ashes of all higher plants, although it 

 has been definitely proved, by the results of water-cultures and 

 of experiments made in prepared soils, that they are not indis- 

 pensable for the growth and for the full and complete develop- 

 ment of higher plants and of the crops we cultivate. Regarding 

 the physiological functions of these three elements and their 

 compounds in the plants, nothing definite is known. 



Of special interest in their relation to plant life is the group 

 of alkali metals : Lithium, sodium, potassium, rubidium, and 

 Ccesium. I\)tassitim is the typical element of this group, and 

 we know more of its functions in the system of plants than of 

 the other elements. The rapid and enormous growth of tlie 

 industry of the potash fertilisers furnishes striking evidence of 

 the practical application of the results of scientific research to 

 agriculture. 



In the order of the natural classification of elements 

 potassium has its place between sodium and rubidium. Both 

 these elements occur frequently in plants, although it has been 

 sufiiciently demonstrated by the results of water-cultures and 

 soil experiments, that they are not indispensable constituents of 

 the food of land plants. They may enter the system of plants 



* The '■ coi)perplant " of North Queensland (Polyrarpcra spiriostilis) 

 contains as much as .56 per mille of copper in the dry plant substance. 

 Prospectors conclude from the occurrence of this plant that cupriferous 

 deposits must he near. 



t Zinc has been observed in the ashes of Viola calainiiiaria, .^rowinff on 

 the Calamine Hills of the Rhenish Province. 



± Manganese is a never-failing constituent of the ashes of the Conifera. 

 in some of which the amount of trimanganic tetroxide rises to 40 per cent, 

 of the weight of the ashes. A large number of analyses of the ashes of 

 various portions of pines from different parts of the Cape Peninsula 

 ' were made some years ago in the Chemical Laboratory of the South 

 African College. The results of all these determinations showed that 

 oxide of manganese was the predominant constituent in all these ashes. 



