AMMONIA. 171 



is too little known, and, making the largest allow- 

 ance, probably too minute, to permit us to consider 

 it as an important source of hydrogen to the general 

 vegetation of the globe." Ammonia is, however, a 

 powerful agent in hastening the fermentation of 

 such materials as are to become plant-food. This 

 it does, according to some authors, directly, and to 

 others, by acting as food to the little fungi which 

 do the work. The value of this compound has, no 

 doubt, been greatly exaggerated by some writers, 

 who have estimated the worth of fertilizers accord- 

 ing to the amount which they contained. It is true 

 that it acts as a stimulant to plants, and perhaps 

 as a solvent for humus. As a writer in the Gar- 

 deners' Magazine states : " Notwithstanding Liebig, 

 Johnston, and Schlieden object to this, on account 

 of the ease with which the humates are decomposed, 

 yet this process may be going on constantly, and, 

 being immediately absorbed by the roots of the 

 plant, this may aid it in building up its structure. 

 But while Liebig argues that ammonia is derived 

 from the air, there seems to be abundant evidence 

 that a portion is also received from the soil. Yet 

 the fact, as stated by some, that ammonia is fur- 

 nished exclusively from the soil, cannot be correct. 

 Both supply it, probably in varying proportions, 

 according to the necessities of the plant." 



Therefore the cultivator should be careful to 

 preserve this extremely volatile substance in his 



