226 Journal of Agricultural Research voi.iv, N0.3 



under experimental conditions that the question may well be raised 

 whether such functions are equally performed under what might justly 

 be termed "abnormal conditions." 



It is ordinarily assumed that the natural condition for A. chroococcum 

 is the one in which the organism is obliged to fix nitrogen, since the 

 name "nitrogen fixer" is applied to it. We know now, as a result of 

 considerable work on the part of a number of scientists, that the growth 

 of A. chroococcum is stimulated by the presence of small quantities of 

 nitrates, and we know% moreover, that A. chroococcum has the power, 

 according to Beijerinck and Van Delden (3), to transform nitrates directly 

 into ammonia, and that, according to Sackett (16, p. 38-39), it forms 

 more of the characteristic pigmentation when grown in a medium con- 

 taining 0.5 per cent of sodium nitrate than in a medium poor in, or free 

 from, nitrates. 



We know also from Sackett (16, pp. 38-39) that ammonium chlorid, 

 ammonium sulphate, asparagin, and peptone do not have the same 

 effect upon this function. The quantity of sodium nitrate used by this 

 author is five times stronger than the one used in ordinary denitrification 

 experiments. 



Since this work indicates that a highly oxidized nitrogenous material, 

 such as a nitrate or nitrite, is the only one that seems to accentuate 

 growth and that this same material is attacked and consumed by A. 

 chroococcum, are we not justified in belie\ang that the condition of life 

 presenting these compounds as foods might constitute a favorable and 

 perhaps an optimum or normal condition for development? In other 

 words, A . chroococcum may be a nitrogen fixer under only such condirions 

 as those which we call "normal" — i. e., when a lack of soluble nitrogenous 

 food is present — and a denitrifier when such conditions are changed — i.e., 

 when there is a possibility for it to consume nitrate under "naturally 

 normal" conditions. It is well known that this micro-organism is a 

 facultative nitrogen fixer, but which is its normal and which its abnor- 

 mal function is as yet an unsolved problem. A cytological study might 

 possibly throw some light on the question. Appreciable changes in 

 structure, detectable by appropriate methods, might accompany changes 

 in physiological functions. An example of this kind of change is given 

 in the recent work by Nello Mori (13), in which he finds that the cultiva- 

 tion of Caryobacterium equi (a pathologic form) on carbohydrate or alco- 

 holic media individualizes in the cells of the organism a so-called nucleus, 

 which was not visible in cells grown on peptone medium. 



A study of the change due to en\'ironment in a unicellular organism 

 will quite naturally simplify a corresponding study in higher plants, in 

 which there have been so much dissension and contradiction. Before 

 undertaking this study we should determine the nature of the cell con- 

 stituents which are capable of undergoing changes \vith variation in 



