FORBES: MINERAL ELEMENTS IN NUTRITION 431 



a stock on which to graft Citrus for culture on the dryer types 

 of soil. The other species, Pleiospermium dubium, was dis- 

 covered growing on limestone hills in western Java and may 

 perhaps be able to endure more lime than the stocks now com- 

 monly used in citrous culture. Certainly both species of Pleio- 

 spermium should be introduced into this country and tested 

 as stocks. In view of its primitive and polymorphic nature it 

 is possible that P. dubium may hybridize with Atalantia or with 

 some other true citrous fruit. 



PHYSIOLOGY. — Studies on the mineral elements in animal 

 nutrition. 1 E. B. Forbes, Ohio Agricultural Experiment 

 Station. 



As agricultural scientists, our interest in the mineral elements 

 lies in that larger intermediary metabolism between the soil 

 and the sea which begins with the weathering of the rocks, 

 includes the whole of plant and animal metabolism, and ends 

 with the formation of new rocks. Throughout this vast sweep 

 of chemical change the mineral elements occupy a unique and 

 dominating position, entering in essential ways into every 

 process and exerting an influence in metabolism entirely out 

 of proportion to the amounts in which they are involved. 



In a large and general way life may be regarded as a coordinated 

 system of responses to electrical stimulation. The ions, and 

 especially the inorganic ions, are the bearers of this electricity, 

 and it is because of this fact that they are able to play a leading 

 role in the direction of the whole process of metabolism. Gus- 

 tav Mann says, " So-called pure ash-free proteids are chemically 

 inert and in the true sense of the word, dead bodies. What 

 puts life into them is the presence of electrolytes." 



This, then, is the basis of our interest. More specifically, 

 this subject concerns us because the mineral elements of soil 

 fertility — of plant nutrition — supply the mineral nutrients of 

 animals. All of those conditions of growth of plants, as to 



1 A lecture delivered before the Washington Academy of Sciences, April 21, 1916. 



