OF PLANTS BY MANURING. 55 



fore they have attained to full maturity, accords en- 

 tirely with this statement. 



If, however, nitrogen is to be rendered fit for the 

 food of plants, it must be first converted by putre- 

 faction and decay into ammonia (or nitric acid), or, 

 to speak more correctly, into ammoniacal salts (or 

 nitric acid salts). These combinations are very ea- 

 sily and rapidly absorbed by plants ; either by their 

 roots, if the ammonia is found in the earth, or by 

 their leaves, if it is contained in the air surrounding 

 them. From this circumstance fresh bone-dust, un- 

 decayed animal excrement, undecomposed urinous 

 liquids, etc., operate far more slowly than when 

 brought on to the field after having previously un- 

 dergone putrefactive fermentation. In the latter 

 state they contain ammonia (putrid nitrogen) al- 

 ready formed, to which the plant can help itself at 

 once ; in the former case, this transformation of the 

 azotized substances takes place in the ground, and 

 the plant must wait until it is in progress, before it 

 obtains ammonia. If this conversion, which will be 

 more fully explained in the fifth and sixth chapters, 

 is of long-protracted duration, — as is the case, for 

 example, in very dry weather (from deficiency of 

 moisture), or in very heavy soils (from deficiency of 

 air), — then it may happen that this manuring pro- 

 duces during the first year no effect whatsoever ; for if 

 the favorable moment, that of most vigorous growth, 

 has once gone by in a plant, the richest nourishment 

 can no longer render it assistance. The extraordi- 



