116 THE COMPOSITION OF CEOPS IX 



nearly twice as much phosphoric acid as a crop of oats, he would 

 make a very great mistake. He has only, however, to give due 

 consideration to the amount of the last item (silica) in the 

 respective columns, in order to see that such a conclusion would 

 be erroneous. Of 100 parts of the ash of oats, more than two- 

 fifths, or only something less than one-half, consists of silica, 

 against only about 3 J per cent, of the same in the ash of wheat ; 

 that is the ash of oats has an excess of silica to the amount 

 41 per cent., or more than two-fifths of the whole. But it may 

 be said, if 41 parts in 100 of the ash of oats consist of this 

 comparatively valueless matter, silica, the remaining valuable 

 constituents, phosphoric acid, potash, and magnesia, must needs 

 be less in oats than in wheat, which is not contaminated (so to 

 speak) with such an excessive amount of that substance. But, 

 neither is that so, because we find that this excess of silica in 

 the ash of oats is only a sort of incidental make-weight which 

 necessarilv results from the silicious shell or husk which 

 adheres to the oat grain in its ordinary state, and, consec^uently, 

 in the state in which it is taken for analysis. If w^e reduce 

 2016 lbs. of wheat, and also 1920 lbs. of oats to ashes, we 

 get on an average 34'3 lbs. of ash from the former, and 

 57 '6 lbs. from the latter ; that is, the oats give more ash by 

 two-fifths than the wheat. But these two-fifths are just the 

 silica resulting from the oat shells. If we deduct two-fifths from 

 57'6, we have 34*5, or as nearly as may be the same amount of 

 ash as the wheat affords. In point of fact, we find that average 

 crops of wheat and oats, afi'ord very nearly the same amount 

 and relative proportions of their more valuable constituents — 

 phosphoric acid, potash magnesia, and sulphuric acid. Taken 

 weight for weight the wheat generally yields a little more of the 

 three first-named ingredients than oats. Nor do average crops 

 of these two cereals difi'er materially in the amount of nitrogen 

 whicli they require. It will be observed that in the crops per 

 acre that we have assumed, namely 4 quarters of wheat and 

 6 quarters of oats, the difiPerence in the weight of grain produced 

 is only 96 lbs. 



From what has been said, it seems abundantly manifest, first, 

 that not only farmers but others are liable to be misled by these 

 statements of the results of analyses of different crops given in 

 percentages of the ash ; and second, that it might therefore be 

 of some service not only in dispelling tlie misapprehension 

 referred to, but by affording both interesting and practically 

 useful information to farmers and students of agriculture gene- 

 rally, if tabular statements were drawn up of the composition 

 of our most common crops in average produce per acre, — that is, 

 if it were clearly set forth how many pounds' weight of each of 

 the more important constituents of plants these several crops 



