Charles B. Lipman 181 



can be made to fix atmospheric nitrogen in nitrogen-poor or nitro- 

 gen-free solutions with one of the sugars or mannite as a source 

 of energy. Maltose and saccharose do not seem to be nearly as 

 well suited to the growth and development of the organisms 

 tested as lactose, dextrose and mannite, the last seeming to be the 

 most favorable when the organisms are considered as a whole. 

 The largest fixation of nitrogen was 2.94 mg. per gram of mannite 

 fixed by Pseudo-yeast Tulare no. 46b. The next largest 2.74 

 mg. by the Burgundy wine yeast per gram of lactose and the next 

 largest 2.38 mg. per gram mannite by Botrytis cinerea. Several other 

 considerable amounts were fixed by other organisms in mannite 

 and lactose solutions which two seem to be the best suited for the 

 fixation of large amounts of nitrogen in distilled water cultures. 



GENERAL DISCUSSION. 



A careful consideration of the data above given brings further 

 confirmation of the work of other investigators to the effect that 

 the power of fixing atmospheric nitrogen is possessed by many 

 of the lower organisms which differ widely in their character. 

 Though the amounts fixed by them, as shown above, are not as 

 large as those fixed by B. radicicola in conjunction with the legu- 

 minous plants nor yet as large as those fixed by the more vigorous 

 species of the Azotobacter group, they are none the less definite 

 and considerable. To the list of organisms which can fix atmos- 

 pheric nitrogen as shown by former investigations may now be 

 added the true yeasts and the "pseudo yeasts," besides Botrytis 

 cinerea, an organism whose parasitic nature would seem to have 

 deprived it of any nitrogen fixing power whatever. This in itself 

 is a very interesting and striking fact. The fixation of nitrogen 

 seems to have been made easier for the organisms in tap water 

 solutions than in distilled water solutions owing to the small amounts 

 of combined nitrogen present in the former. The nitrogen fixed 

 would, in many cases, seem to have been of a soluble nature since 

 considerable fixation was often noted in solutions where the growth 

 would not seem to indicate it. The conclusions of Duggar and 

 Knudson 1 are therefore not supported by the investigations above 

 described. An effort is now being made by the writer to carry 



1 Science, N. S., xxxiii, p. 191, 1911. 



