134 SOURCE OF NITKOGEN IN PLANTS. 



195. The quantity of Ammonia which is thus supplied to 

 plants, appears sufficient for their ordinary growth. If, how- 

 ever, plants be set in powdered charcoal, sheltered from rain or 

 dew, and watered with distilled water (which contains no am- 

 monia), they do not flourish as they have been stated otherwise 

 to do, but soon become stunted in their growth. This fact 

 proves the great importance of the small amount of nitrogen thus 

 introduced. There are many plants, however, to which a much 

 greater supply of ammonia is necessary, on account of the large 

 proportion of nitrogen, which enters into some portions of their 

 structure ; and these can only be cultivated to advantage, when 

 surrounded by additional sources of this material, such as are 

 afforded by decaying animal matter of various kinds. For ex- 

 ample, corn-grains include a large quantity of starch, which con- 

 tains but little nitrogen, with a certain amount of gluten, of 

 which nitrogen forms a large proportion ; the latter is the more 

 nutritious ingredient of the two ; and it should be the object of 

 the farmer to make the proportion of it as great as possible. 

 This may be effectually accomplished, by such Animal manures, 

 as yield a large supply of ammonia. Thus, whilst corn grown 

 in common vegetable mould contains about 66 parts of starch in 

 every hundred, and only 9J of gluten, that which had been 

 manured with blood or urine was found to contain 45 parts of 

 starch, and 35 of gluten. It is by the use of a rich animal 

 manure termed guano, that the barren soil on the coast of Peru 

 is rendered fertile ; this guano is collected from several islands 

 in the South Sea, on the surface of which it forms a layer of 

 several feet in thickness ; and it consists of the excrements of 

 innumerable sea-fowl, which resort there during the breeding 

 season. It is sufficient to add a small quantity of guano to a 

 soil, which consists only of sand and clay, and which previously 

 contained not a particle of organic matter, in order to produce 

 the richest crop of maize. 



196. Many kinds of soil have the power of absorbing am- 

 monia like carbonic acid, from the atmosphere ; and thus add to 

 the supplies which the plant obtains by its roots, so as to dimi- 

 nish the necessity for animal manure. Of this kind is gypsum, 



