484 
Report of Experiments on the Growth of Wheat. 
the mineral manure gave larger amounts of increase, but at a 
very much diminished rate in proportion to the ammonia em- 
ployed. Thus, a manure containing ammonia-salts and soluble 
mineral constituents, but neither silica nor organic matter yielding 
carbonic acid or other compounds of carbon within the soil, gave, 
for many consecutive years, more produce than an amount of farm- 
yard manure supplying annually more of every mineral con- 
stituent, including silica, more nitrogen, and more carbon, than 
the total produce removed from the land. 
7. Nitrate of soda, in amount containing about the same 
quantity of nitrogen as 400 lbs. of ammonia-salts, used in con- 
junction with the same mineral manure, gave nearly as much corn, 
and more straw and total produce, than the farmyard manure. 
8. No beneficial effect resulted from the use as manure of 
organic matter yielding by decomposition carbonic acid, or other 
compounds of carbon, within the soil. In fact, although a crop of 
wheat equal to the average produce by farmyard manure would 
contain about 2000 lbs. of carbon, the plant seems practically 
independent of any supply of carbon by manure, being able to 
assimilate this large amount, either by its roots or its leaves, from 
the atmospheric sources, if only mineral constituents and nitrogen 
be supplied to the soil in sufficient quantity and in available form. 
Other cultivated plants of the Graminaceous family, such as 
barley, and the grasses of our meadows and pastures, appear to be 
equally independent of a supply of carbon by manure. Root- 
crops, and probably some other of our agricultural plants are, on 
the contrary, very dependent on a supply of carbon from decom- 
posing organic matter within the soil. 
9. The carbonaceous organic matter of the farmyard manure 
used in the experiments, if not without effect, was obviously at 
any rate unnecessary ; and the increase obtained by the use of 
that manure was no doubt mainly due to its large, but compara- 
tively slowly available, supply of ammonia, or nitrogen in some 
other form, and mineral constituents. 
IV. Amount of Increased Produce obtained for a given 
Amount of Ammonia supplied in Manure. 
It has been shown that full crops of wheat cannot be grown 
unless there be a liberal available supply of mineral constituents 
within the reach of the plant, and further, that such supply is 
ineffective unless ammonia, or nitrogen in some other available 
form, be also liberally provided within the soil. In our con- 
cluding observations reference will be made to the various means 
at the farmer's command of keeping up the necessary supplies of 
both the mineral constituents and nitrogen. But as the purchase 
