THE ATMOSPHERE AS A SOURCE OF NITROGEN. 49 



able for the direct nutrition of ordinary plants, is made available for 

 the use of leguminous crops. 



It is not so generally knoAvn that there are in soils certain species 

 of bacteria not connected with the roots of plants which also possess 

 the facult}^ of taking up the nitrogen of the air and making it over 

 into plant food. The extent of the distribution of these organisms and 

 the amount of nitrogen fixation effected by them are not fully known, 

 but the fact that such action does take place and that the bacteria 

 causing it occur in many localities has been well established by the 

 experiments cf several investigators. The bacteria of this class most 

 fully investigated are Clostridium pasteurianum-^ Azotohacter chro- 

 ococciim^ and several other species of this latter genus. 



It has been shown also that certain fungi, such as Penicillium 

 glaucum., possess this same power of assimilating atmospheric 

 nitrogen. 



After the writer had discovered the mycorrhizal fungus of the 

 swamp blueberry in December, 1907, and while he was making obser- 

 vations on it, his attention was called to the work of Miss Charlotte 

 Ternetz on the mycorrhizal fungi of certain related European plants. 

 Miss Ternetz published in 1904 a paper ° in which she made the pre- 

 liminary announcement that a fungus isolated from the roots of the 

 European cranberry {Oxy coccus oxy coccus) had developed pycnidia 

 and that the mycelium produced from spores from these pycnidia when 

 grown in a nitrogen-free nutritive solution, but with full access to air, 

 showed upon analysis that it had assimilated free atmospheric nitro- 

 gen to the extent of O.G per cent of the dry weight of the mycelium. 

 The fungus consumed only one-eighth as much dextrose in assimi- 

 lating a given amount of nitrogen as was consumed by Clostridium 

 pnstevriajami. Similar but not identical fungi were isolated from 

 other related plants. 



In 1907, in a more detailed account of her investigations,^ Miss 

 Ternetz described, as new species of Phoma, five pycnidia-bearing 

 fungi bred from the roots of the European cranberry {Oxy coccus 

 oxycoccus) ^ the marsh rosemary {Andromeda polifolia), two species 

 of heather {Erica tetrcdix and E. cariiea)^ and the mountain cranberry 

 {Vacciniiim vitisidaea). She was unable to demonstrate absolutely 

 that these fungi were identical with the endotrophic mycorrhiza of 

 the host plants because (1) it was extremely difficult to observe the 

 fungous threads of the internal mycorrhiza grow through the cell 

 wall of the rootlets into the culture medium without, and (2) be- 



° Teruetz, Charlotte, Ph. D. Assimilation des atmospharischeu Stickstoffs 

 durch einen torfbewohnenden Pilz. Berichte der Deutschen Botanischeu 

 Gesellschaft, vol. 22, 1904, pp. 267-274. 



* Ternetz, Charlotte, Ph. D. Ueber die Assimilation des atmosphiirischen 

 Stickstoffes durch Pilze. Jahrbiicher fiir Wisseoschaftliche Botanlk, vol. 44, 

 1907, pp. 353^08. 



54708°— Bull. 193—10 4 



