NITROGEN : WHY AND WHERE CROPS MUST GET IT. 203 



supply of these organisms can make their wa}", this absorption of 

 nitrogen ceases. 



This useful work of these organisms goes on most rapidly under 

 just those conditions of the soil and air that are most favorable for 

 vegetable growth ; nitrogen is most rapidly absorbed in this wa}' in 

 summer, and the operation does not go on in winter. Berthelot 

 estimated that at least from 25 to 30 pounds of nitrogen may be 

 absorbed, in the season from April to October, by the soil of an 

 acre. This seems to me to be one of the most curious and inter- 

 esting discoveries that has been lately made in regard to this nitro- 

 gen question ; and it is the more interesting when regarded in 

 connection with the fact that another kind of bacteria work upon 

 the insoluble and uuassimilable nitrogen compounds in the soil ; 

 slowlj' converting them into nitrates, than which there is no better 

 form of nitrogenous plant food. As friends or foes, tliese very 

 minute beings stand in close relation to our comfort and hapi)iness. 

 From their apparent connection with many dangerous animal dis- 

 eases, we have come to regard them much more as enemies than 

 as friends ; and since it is now quite clearly proven that the}' are 

 the cause of the pear blight, and their baneful influence in connec- 

 tion with diseases of the vegetable kingdom is thus established, we 

 have become still less kindly disposed towards them ; but by the 

 time that all the phases of their work shall have been clearly made 

 out, we may find that its sum total shows a beneficial balance in 

 our favor. 



To sum up the whole matter — we find that there are five ways 

 in which vegetation may get nitrogen more or less directly from 

 the atmosphere : — 



First. By means of the ammonia compounds and nitrates, 

 already formed there, and which are conveyed to the foliage and 

 to the soil by the fogs, dews, and rains, and to the soil by the 

 snows of winter. 



Second. B}' the direct absorption of gaseous ammonia com- 

 pounds from the air by the foliage. 



Third. By the absorption of gaseous ammonia compounds by 

 the soil, in the same manner that any porous body will absorb any 

 gas to which it is exposed. 



Then follow the two ways which involve the direct conversion of 

 free nitrogen into nitrogen compounds, but not by the plant itself: 



Fourth. Through some electrical action, in the presence of pro- 



