60 



SCIENCE 



[N. S. Vol. XXXI. No. 785 



havior of Sterigmatocystis nigra in rela- 

 tion to its assimilation of nitrogenous 

 material. This fungus has the power, to a 

 limited extent at least, of assimilating free 

 nitrogen from the air. Stimulation ap- 

 pears to diminish this ability and to cause 

 the fungus to rely more largely upon the 

 nitrate fed to it : or at any rate the organ- 

 ism does not excrete into the liquid sub- 

 stratum as large an amount of waste nitrog- 

 enous products as does the normal. Fur- 

 thermore, the nitrogenous content of 

 the dry substance of the plant is not af- 

 fected one way or the other. In regard to 

 the nitrogen supplied in combined form, 

 there is less thrift in the stimulated than 

 in the normal growth, but, on the other 

 hand, the total amount of nitrogen in- 

 volved, including that excreted as waste 

 into the substratum, is less in the former 

 than in the latter case. This whole ques- 

 tion is, of course, a hugely complicated one 

 and in the light of our relatively slight 

 knowledge of nitrogen metabolism one 

 which should be approached with caution. 

 But it is evident that the problem is of 

 great importance. 



In this connection it is apropos to quote 

 from practically the only investigation we 

 have which touches on this point. 



To explain the reason for the activity of the 

 organism along these lines there are these sug- 

 gestions: one that the fixation of free nitrogen 

 and its excretion in combined form may be a 

 function connected with fructification, since stim- 

 ulated felts do not produce spores; another . . . 

 is that the stimulated crop, driven to its most 

 rapid metabolic activity by the stimulant, is 

 forced to consume its carbohydrate more econom- 

 ically and therefore finds less energy to use in 

 effecting the combination of the relatively inert 

 and difBeultly combinable nitrogen, and so must 

 use the more readily assimilable compound nitro- 

 gen; or again it may be that since by the presence 

 of the stimulant the fungus can consume carbo- 

 hydrate more thoroughly and with less waste, 

 therefore it finds in what would be a normal 

 amount under ordinary circumstances a more than 



necessary amount under the favoring influence of 

 the stimulant, which, of course, would be then 

 potentially a too great supply, and the result 

 would be over feeding in this direction and there- 

 fore there would be a tendency to lessened activity 

 in expending energy for nitrogen combination. 

 This last hypothesis is in accord with conclusions 

 that have been reached on the activity of the root 

 tubercle bacteria in fixing nitrogen when well 

 supplied with nitrogen compounds, but not in 

 accord with the results of those who find that the 

 fixation of nitrogen is directly proportional to the 

 amount of sugar at hand. 



After consideration of the whole matter, 

 one is inclined to the opinion that, after all, 

 since less nitrogen passes through the fun- 

 gus for the amount of dry substance 

 formed, there is economy in nitrogen as 

 well as in carbohydrate metabolism in a 

 stimulated growth. And taking it all in 

 all, there seems to be sufficient evidence for 

 maintaining that under chemical excitation 

 of optimum intensity the waste involved in 

 mere cell formation, at least, is not so great 

 in stimulated as in unstimulated proto- 

 plasm. 



In this connection there arises at once 

 another question of great importance, 

 namely, what influence stimulation has on 

 enzymatic activity. While the data on this 

 point are still incomplete, it is permissible 

 here to make reference to certain results 

 not yet completed which throw some light 

 upon this phase of the matter. Here Eigain 

 Sterigmatocystis nigra is valuable for ex- 

 perimentation. In common with many of 

 its kind, this fungus can live on a great 

 variety of substrata, its ability to do so 

 being due in large measure to its versatility 

 in the excreting of an enzyme appropriate 

 to the particular compound on which it is 

 growing. Thus it will produce mal- 

 tase when grown on maltose, sucrase 

 when grown on saccharose, inulase on 

 inulin, amylase on starch, etc. A quan- 

 titative estimation of its hydrolyzing power 



