COMPOSITION OF CULTIVATED CROPS. 



79 



TABLE III. 



These do not represent the exact composition of the 

 ash from the above crops, in all cases, but should be 

 considered only approximations. In different situa 

 tions, there is frequently a considerable variation in 

 composition; this does not, however, affect the general 

 character, where the soil contains a full supply of 

 necessary substances. The ash from healthy potatoes, 

 for instance, never resembles that from a flourishing 

 crop of wheat. The table then may be regarded as 

 approaching sufficiently near the truth for all practical 

 purposes. 



SECTION II. ON THE SEPARATION OF PLANTS INTO CLASSES, 

 ACCORDING TO THE COMPOSITION OF THEIR ASH. 



I have inserted in comparison with the grain of 

 wheat, an analysis of ash from the straw also, as an 

 illustration of the difference in the substances which 

 they respectively draw from the soil. 



a. It will be noticed that in the ash from the grain, 

 phosphoric acid is the chief ingredient, making up 

 nearly half : potash also is in large quantity, being 



