90 THE CULTURE OF FARM CROPS. 



the writers garden at the present time is a bed of red cab- 

 bage ; through the center of which flows a drain from the 

 yard in which the manure from the horse stable is kept. On 

 both sides of this drain, for about 3. feet, the red cabbages 

 are blue : and their growth is far more luxuriant than that 

 .of other plants distant from the drain. Is not this a dis- 

 tinct illustration of the fact that the ammonia from the li- 

 quid manure; in which it is shown to be abundant by the 

 litmus paper test ; is absorbed by the cabbages and acts up- 

 on the coloring matter with its usual effect? 



In all these cases however the proof is not decisive; but 

 it is quite sufficient to make it appear that the probabilities 

 are all in favor of the belief that ammonia does enter into 

 the tissues of plants when brought in solution in water to 

 the roots and to justify us in holding this belief. But ac- 

 tual proof is wanted before this can be asserted as a fact. 

 The changes which occur in nature are so involved ; so in- 

 tricate ; so sudden ; and so unexpected when experience is 

 at fault ; that we should hesitate to found a belief upon any 

 but the strongest evidence, or to base a principle, or a law 

 for our guidance, upon anything but accurate and well de- 

 termined knowledge. So far as the question under consid- 

 eration is concerned this knowledge is wanting ; but a mass 

 of observed facts tending thereto is all that w r e possess. 

 Other soluble compounds of nitrogen are formed during the . 

 decay and oxidation of animal substances and actually ex- 

 ist in the liquid manures of the stable and yards, and they 

 are likely to be absorbed by the roots of plants when ap- 

 plied to the soil. Thus urea, a compound of carbon, hy- 

 drogen, nitrogen and oxygen, and containing about one- 

 third of its weight of nitrogen, exists abundantly in urine, 

 and by its decomposition produces carbonate of ammonia. 

 Being very soluble this substance may enter with water in- 

 to the roots of plants and be decomposed within the tissues 

 and made to give up its nitrogen. The same may be ap- 

 plied to other compounds of nitrogen ; so that while the fact 

 that animal manures are very beneficial to the growth of 

 plants, may be considered as favoring the probability that 



