ABSORPTION OF FREE NITROGEN 107 



Nitrogen Nutrition of Green Plants. — It is the belief of 

 botanists that green plants obtain their nitrogen chiefly 

 in the form of nitrates, though ammonium salts may be 

 utilized to some extent by certain plants at least. Excep- 

 tions to this general rule are those plants provided with 

 root tubercles (and the bog plants and others which have 

 mycorrhiza?) . These plants obtain their nitrogen in the form 

 of organic compounds made for them by the bacteria grow- 

 ing in the tubercles. That nitrogen circulates throughout 

 the structure of plants in organic combination is certain. 

 There does not appear to be any reason why similar com- 

 pounds which are soluble and diffusible (amino-acids?) should 

 not be taken up through the roots of plants and utilized 

 as such. It seems to the author that this is very probably 

 the case. Arguments in favor of this view are: (1) The 

 nitrogen nutrition of leguminous and other plants with root 

 nodules. (2) The close symbiosis between "Azotobacter" 

 and similar nitrogen-absorbing bacteria and many species 

 of algse in sea water at least. (3) The vigorous growth of 

 plants in soils very rich in organic matter, which inhibits 

 the production of nitrates by the nitrous-nitric bacteria 

 when grown in culture, and possibly (?) in the soil, so that 

 nitrates may not account for the vigorous growth. (4) The 

 effect of nitrate fertilizers is to add an amount of nitro- 

 gen to the crop much in excess of the amount added as 

 nitrate. (5) The most fertile soils contain the largest num- 

 bers of bacteria. . The doctrine that nitrates furnish the only 

 nitrogen to plants was established before the activities of 

 bacteria in the soil were suspected, and, so far as the author 

 is aware, has not been supported by experiments under 

 conditions rigidly controlled as to sterility. 



It would seem that one of the chief functions of soil bac- 

 teria is to prepare soluble organic compounds of nitrogen 

 for the use of green plants and thus to make a "short cut" 

 in the nitrogen cycle (p. 96), as now believed in, direct 

 from the "decomposition bacteria" to green plants. 



Experiments have been made by different observers in 

 growing seedling plants of various kinds in water culture 

 with one or in some cases several of the amino-acids as 



