334 ASSIMILATION. 



in the soil can be turned to a very important account by the 

 plant. 



877. Nitrogen used by wild and cultivated plants. From the 

 sources described, wild plants obtain a sufficient supply of 

 available nitrogen. In some localities, notably in portions of 

 the tropics and along the rich alluvial deposits of rivers, the 

 stores of available nitrogen are so abundant that all vegetation 

 flourishes with great vigor, and even cultivated plants, which ap- 

 pear to be more exacting than wild plants in their demands for 

 nitrogen, can obtain an adequate supply. Further, it has been 

 abundantly shown b}- the long-continued experiments at Rotham- 

 sted, that the same soil, unenriched by additions of manures, can 

 yield even after twenty-five years enough nitrogen for the needs 

 of fair or moderate crops. 



878. In the ordinary cultivation of plants it is profitable 

 to augment in some way the supply of nitrogen in most soils. 

 Under some circumstances this augmentation can be accom- 

 plished to a certain extent by mere tillage or by the exposure 

 of fresh portions of soil to the action of the atmosphere. But 

 it is usually effected by the employment of natural or artificial 

 manures. The former consist of the excrementitious matters 

 of animals or of the waste products from plants. These ex- 

 crementitious matters represent a large part of what the ani- 

 mals have consumed, and must have come either directly 

 or indirectly from the vegetable kingdom ; hence they only re- 

 store to the soil that which plants had at some time removed 

 therefrom. 



In the preparation of artificial fertilizers an effort is made to 

 provide for the plant the mineral and nitrogenous matters which 

 it requires. A large proportion of these fertilizers are composed 



throughout, and can leave no doubt that, under the conditions of his trials, 

 there was practically no utilization of the soil nitrogen by the plants. 



On the other hand, experiments by Wolff (Chemisch.-Pharniaceut. Central- 

 Blatt, 1852, p. 657), Johnson (Peat and its Uses, 1866, p. 79), and Storer 

 show that under certain conditions the plant can avail itself of the nitrogen 

 organically combined in the soil. The works of the above authors, which are 

 only a few of those bearing on this important matter, will place the student in 

 possession of the methods of experimenting. 



Storer's interesting communication in the Bulletin of the Bussey Institu- 

 tion (vol. i., 1874, p. 252), " On the Importance as Plant-food of the Nitrogen 

 in Vegetable Mould,' 7 gives not only an account of his experiments but also 

 a forcible presentation of the principal arguments in favor of the belief that 

 the "soil-nitrogen " (that is, the nitrogen in vegetable mould) is by no means 

 inert. 



