THE LAW OF CONCORD IN NATURE 33 



Dr. E. J. Russell refers to a generalisation made by Liebig in 

 1840, with regard to plant nutrition to the effect that the true 

 function of manure is to provide, not organic matter, but mineral 

 constituents, which the chemists had ignored. 



This discovery of Liebig, according to Dr. Russell, was " a 

 brilliant stroke. It enabled us to reduce the whole art of 

 manuring to an exact science." Before 1840, as this authority 

 tells us : 



The practical man knew that farm-yard manure was the great ferti- 

 liser ; he also knew that other substances as bones, salt, etc., had, in certain 

 circumstances, considerable fertilising value. The most obvious facts were 

 the large amounts of organic matter in the best manures ; and it is only 

 natural that chemists and physiologists should have connected these 

 and argued that the object of the manure was to furnish organic matter 

 for the plant. 



But Liebig's " brilliant stroke " of discovery brushed aside 

 this " obvious connection " and proclaimed that it is the mineral 

 constituents that are indispensable and must be supplied to the 

 plant, i.e., in my more generalised terminology, that the plant's 

 well-being depends upon " cross-feeding/' i.e., on its draft on 

 the inorganic kingdom. True, Liebig had left something out. 

 Thinking that the requirements of a plant could be gauged by 

 the composition of the ash, he overlooked the fact that, " for 

 practical purposes/' it was necessary to add nitrogen as well 

 before complete growth could be obtained. For, a complete 

 growth depends upon a complete diet, as a complete heredity 

 depends on a full measure of contribution from the symbiotic 

 environment which, in this instance, is furnished by nitrogen 

 specially elaborated for the plant by friendly bacteria. Dr. 

 Russell tells us that we may take it as established that crops 

 can be grown satisfactorily and indefinitely by supplying proper 

 quantities of suitable compounds of nitrogen, phosphorus and 

 potassium, and he would call this the first principle of Crop 

 production. The first principle of Crop production is, I should 

 claim, an integral part of the greater generalisation that " cross- 

 feeding " is the ideal method of obtaining these essentials of 

 diet for all organisms, and I maintain, that the work of the 

 world is best done on " cross-feeding." 



And that such a bio-economic and for that matter widely 

 generalised statement is called for and well justified, is borne 

 out by Dr. Russell's account of the successive steps of 



