YII. NITROGEN ASSIMILATION BY ISOPYEllI 

 BITERNATUM. 



A PRELUIINARY NOTICE. 

 D, T. MacDougal. 



Probably the most abstract problem confronting the plant 

 physiologist at the present time is the determination of the 

 manner in which the higher plants acquire their supply of 

 nitrogen. Until within the last sixteen years all plants were 

 supposed to be entirely dependent upon the fixed nitrates of 

 the soil. About 1880 began an era of investigation remarkable 

 for its important results in the discovery of many of the essen- 

 tial features of this phase of plant nutrition. Since the above 

 date more than three hundred memoirs and double the number 

 of lesser papers on the subject have made their appearance 

 from the laboratories of the world, and it continues to absorb 

 the attention of a large number of the foremost investigators. 



The results so far attained show that bacterial forms, fungi, 

 algae, hepatics, and to a limited extent the higher plants may 

 make use of free nitrogen. The conditions of the absorption of 

 free nitrogen by the higher plants are not understood farther 

 than the fact that they are under no circumstances independent 

 of the fixed nitrates. The delimitation of this capability of the 

 higher plants to assimilate free nitrogen will doubtless claim 

 much attention for some time to come. It seems probable in 

 the light of the most recent researches that this capability will 

 be found to be more highly developed in certain groups than in 

 others, and that within these groups individual species will 

 exhibit marked maxima. 



A large part of the attention to the general subject during 

 the last decade has been paid to the correlations by which the 

 products of the nitrogen assimilation of the lower forms are 

 made available to the higher plants — a series of facts of the 

 widest biological significance. As types of these correlations, 

 may be mentioned the activity of the soil bacteria resulting in 

 the maintenance of the supply of fixed nitrates, while" bacteria,. 



