76 Recent Publications on Manures, 



?>\ lb. of flour, made from the wheat grown with nitrates, pro- 

 duced 4 lb. 14 oz. of bread; while the same quantity of the 

 other produced only 4 lb. 4 oz. The application of these salts, 

 he thinks, acts as a stimulant to the plant; as in some cases, 

 where the nitrate of soda was applied last spring, and where it 

 had produced a most marked and decided effect, it was found, 

 that, after the grass was cut and the produce harvested, the after 

 growth was a long time before it came away : apparently the 

 plant had suffered from over-excitement, as the grass not manured 

 with the nitrate was afterwards, for a considerable time, the 

 more luxuriant. Professor Daubeny has stated his opinion, also, 

 that nitrate acts as a stimulant to the plant, causing more other 

 food to be assimilated. His views on the origin, &c, of ammo- 

 nia, I noticed in a former essay. Professor Johnston says, 

 the nitrogen in any crop is small in amount, but perhaps not the 

 less essential. The nitrogen, he says, must all have been origi- 

 nally from the air, from which it has been furnished to coal 

 and other matters containing vegetable or animal remains. The 

 nitrogen of the air being partially soluble in water, he thinks 

 part of the nitrogen of plants may be got from this source. He 

 calculates all the water falling on the soil in a year ma}' contain 

 28 lb. of nitrogen, and probably one third of this is absorbed. 

 Ammonia and nitric acid are both, he thinks, sources of nitrogen 

 to plants : no doubt, he says, more nitric acid enters than is 

 fixed, but it is the same with ammonia. Nitrates, he says, have 

 the same effect applied to the soil as ammonia, in increasing the 

 gluten of wheat ; the effect is the same in kind, though less in 

 degree. Great part of the effect of ammonia, he thinks, consists 

 in its aptitude to decompose, yielding at one place of the plant 

 hydrogen, and at another nitrogen, from the circulating fluid, 

 as required, and again forming ammonia where the consti- 

 tuents are not needed : in the same way as water is decom- 

 posed, and yields now hydrogen, and now oxygen, as required. 

 On the question, whether leaves absorb nitrogen, the professor 

 notices Boussingault's experiments, in which the nitrogen of the 

 air was not diminished, but rather increased, by the action of 

 the leaves ; but absorption and transpiration might both be in 

 action. The increase must have been from the latter, but it 

 might be more than shown. The ammonia in tobacco leaves, he 

 thinks, may be formed from nitrogen. 



Of the experiments on manures at Dankeith, the seat 

 of Colonel Kelso, near Symington, when I called there in 

 July, the gardener, Mr. Hay, showed us several which were 

 making with different kinds. Rape dust he used in the pro- 

 portions which had been used the year before by Mr. Fle- 

 ming of Barrochan, near Paisley, viz., 1 1 lb. to the drill of 48 

 yards long, exclusive of manure, or about 1 lb. to the 4 lineal 



