v.] PHOSPHORIC ACID AND NITROGEN IN CROP 141 



by the examination of a large number of analyses of 

 barley grain from the Rothamsted plots ; when phos- 

 phoric acid is deficient the intake of nitrogen is not 

 proportionally reduced ; in fact, the grain grown on the 

 plots receiving no phosphoric acid is the richest in 

 nitrogen. 



This point may be further elucidated from some 

 experiments upon wheat made at Rothamsted in 1907; 

 a large number of ears of wheat were marked just as 

 they came into flower, in order to secure that all should 

 be as nearly as possible the same age at starting. A 

 number of these heads were gathered every third day, 

 and the grain was extracted and analysed, so as to trace 

 any progressive changes in composition as the grain 

 formed and ripened. Table XXXVI. shows the ratio 

 of nitrogen to phosphoric acid in such grain from three 

 of the Rothamsted plots — from the unmanured Plot 3, 

 where all the elements of nutrition and particularly nitro- 

 gen are lacking ; from Plot 10, where there is an excess 

 of nitrogen and a great deficiency of phosphoric acid ; 

 and from an adjoining plot under ordinary farming 

 conditions, where phosphoric acid will be relatively 

 abundant. It will be seen that on any plot the ratio 

 of nitrogen to phosphoric acid remains pretty constant 

 throughout the whole development of the grain, but 

 that a different ratio exists for each plot. From this 

 we may conclude that the material which the plant on 

 any particular plot moves from its straw and root to 

 form into grain is the same throughout the development 

 of the grain, but that each plant, according to the soil 

 and manure conditions under which it is growing, 

 builds up a type of grain of a composition special to 

 itself. It is true that the nitrogen and phosphoric acid 

 move into the grain pari passu, and in that sense the 

 phosphoric acid might be regarded as a carrier of the 



