334 ASSIMILATION. 



in the soil can be turned to a very important account bj- the 

 plant. 



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

 sources described, wild plants obtain a sufBeient supply of 

 available nitrogen. In some localities, notabl}- 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 suppl3-. Further, it has been 

 abundantlj- shown bj- the long-continued expei-iments at Eotham- 

 sted, that the same soil, unenriched bj- additions of manures, can 

 yield even after twentj-five jears ei5ough nitrogen for the needs 

 of fair or moderate crops. 



878. In the ordinarj- cultivation of plants it is profitable 

 to augment in some waj" the supply of nitrogen in most soils. 

 Under some circumstances this augmentation can be accom- 

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

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

 it is usually effected bj- the emploj'ment 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 directlj' 

 or indirectlj- 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 pvKCtically no iitilization of the soil nitrogen by the plants. 



On the other hand, experiments by Wolif (Chemisch.-Phavmaceut. Central- 

 Bktt, 1852, p. 657), Johnson (Peat and its Uses, 1S66, 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 comniut:ication 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," 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. 



