254 SCIENCE PROGRESS 



know yet what is the difference in composition between crops 

 of high and of low quality, still less do we know whether the 

 ordinary criteria by which quality is judged are justified when 

 the material comes to be employed in feeding man or stock. 

 The knowledge that we have of the composition of a crop is 

 only what may be termed a first approximation. We know 

 the amount of nitrogen it contains and can determine what is 

 protein and what is non-protein. We can estimate the chief 

 carbohydrates — starch and sugar — but there are whole groups of 

 minor constituents which have not been discriminated though 

 they must play the all-important part in determining what we call 

 quality. With the improved methods of analysis now at our 

 disposal and particularly with our increased knowledge of the 

 nitrogenous compounds of a non-protein nature, it is possible to 

 attack the composition of crops from a much more refined point 

 of view. We shall also have to work out the presence of a 

 number of substances which exist sometimes in very minute 

 proportions — glucosides, essential oils, alkaloids — which we are 

 beginning to learn may have a most potent effect in the nutrition 

 of animals, because they act as stimuli and starters of many 

 forms of vital action. It is recognised, for example, that the 

 grass of one field may have the power of fattening an animal 

 whereas similar grass growing on an adjoining field, though fed 

 to an unlimited extent, will never bring an animal into condition 

 for the market. Our present methods of analysis fail to dis- 

 criminate between the two kinds of grass and until they are 

 refined to the pitch of doing so we cannot make much headway 

 with the finer art of feeding cattle and of utilising the land to the 

 best advantage. It is here that the material afforded by the 

 Rothamsted plots becomes of so much value. We have wheat, 

 for example, grown under conditions of normal manuring and 

 on a minimum of plant food, grown again on an altogether 

 distorted and one-sided nutrition, lacking in phosphates for 

 example or overdosed with an excess of nitrogen. When we 

 are certain of the effects which these variations produce in the 

 composition of a given crop we may deduce the causes of a 

 similar shift of composition found in the produce of ordinary 

 farm land elsewhere. Even such a problem as the susceptibility 

 to disease and its causes finds illustrative material on the 

 Rothamsted plots. For example, certain of the mangold plots 

 are in the majority of seasons devastated by the attacks of a 



