I?s BOTANICAL GAZETTE [march 



more difficull on account of the narrow limits of experimentation to 



which living organisms can be subjected. Although no finally satis- 

 factory conclusions have been reached, a few series of cultures have 

 been worked out with great care. As 1 am for the present comix lied 

 by circumstances to discontinue the work, it is desirable to present 

 the results thus far obtained, with a few final remarks on their pos- 

 sible significance. 



MKTHODS 



The form selected for this work was a strain of Penicillin))! gla»- 

 cum. A number of other molds were tried, but were rejected because 

 they did not thrive well under the conditions of the experiments. 

 Penicillium, which has been used in innumerable physiological inves- 

 tigations, is especially suitable for this work on account of its omnivo- 

 rous habit, anil because many compounds have been studied with 

 regard to their nutritive value for this fungus. The same strain of 

 the mold was used throughout. The stock-cultures were always 

 grown on sterilized bean-stems, so as to avoid any possible temporary 

 influence of the substratum on the strain. 



The culture medium used was a solution of the necessary inorganic 

 salts, of the purest grades obtainable in the market. Except where 

 specially noted, the culture fluid always contained the mineral salts 

 in the same concentration, namely, E gm NH 4 N0 3 , o.5 gm KH,P0 4 , 

 and o.25 8m MgS0 4 , per ioo cc . Potassium chlorid was added in 

 some cases, and the concentration of the magnesium salt was varied 

 in others. These changes are noted in the respective tables. It was 

 the purpose in this work to have the mineral solution alike in all the 

 cultures in order to make the different series exactly comparable. 

 This was carried out, except where special problems occurred which 

 demanded a change from the standard. 



As a source of carbon the following substances were used : alcohol 

 C 9 H s OH), potassium ethyl sulfate ^C\H 5 KS0 4 >. ethyl nitrate 

 C,H s N0 3 ), ethyl acetate ^CH 3 COO(\HA, potassium acetate 

 (CH3COOK), and acetic acid ^CH.COOHb These compounds 

 are all closely related, and have certain radicles in common. The 

 combination of those radicles with various groups has a definite 

 effect upon the mode of reaction of the compounds. By a compara- 

 tive study of a large number of compounds of this nature with regard 



