1019] 



ZELLER AND SCHMITZ — MIXED CULTURES 189 



which the solution diffused. All of the Basidiomycetes grew well 

 upon these sand slopes, and the solution was easily drained from 

 the sand at the end of the period of culture. After two weeks' 

 growth of the fungi the hydrogen ion concentration of the solu- 

 tions was determined according to the methods previously cited. 1 

 In cases where there was a marked stimulation or inhibition of 

 growth between two fungi on the plates, these fungi were then 

 grown on similar sand slopes. After they had made considerable 

 growth the solution was filtered off, sterilized, and prepared 

 for inoculation with the reciprocal fungus. Controls of these 

 solutions were kept uninoculated. The amount of growth of the 

 second inoculation was determined by the dry weight of the 

 fungous mat and the amount of sugar remaining in the solutions 

 estimated. The latter was accomplished by reducing equal 

 amounts of the solutions with equal amounts of Fehling's 

 solution and estimating visually the amounts of copper oxide. 

 The distinctions were so evident that quantitative determina- 

 tions were unnecessary. 



The dry weight of mycelium produced in each case and an 

 estimation of the amount of sugar remaining in the solution after 

 growth of the first and second fungus are shown in table n. 



In some cases it would seem that the carbohydrate content of 

 the nutrient solution upon which a fungus had previously grown 

 might have been the limiting factor for growth. In others, 

 however, this is not true; for example, when L. vialis follows A. 

 niger there is very little growth, although the carbohydrate 

 content was high, while in the control solution upon which no 

 fungus had grown L. vialis made considerable growth and 

 used a greater part of the sugar in the solution. This would 

 tend to indicate that A. niger in its metabolism may have 

 secreted some substance which was toxic to the growth of L. 

 vialis. It is of course quite probable that such toxic substances 

 were formed in many more instances but were destroyed in the 

 process of autoclaving between the first and second inoculation. 



This in general agrees with the conclusions reached by Fulton 2 

 that fungi in their growth show a more marked tendency to grow 



1 Zeller, Schmitz, and Duggar, I. c. 



4 Fulton, H. R. Chemotropism of fungi. Bot. Gaz. 41 : 81-108. 1906. 



