[Vol. 6 



188 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



of the heads of conidiospores of Aspergillus Sydowi when in 

 contact with Merulius pinastri, and the same is true of Asper- 

 gillus niger in contact with A. glaucus. 



As previously mentioned, hydrogen ion concentrations of 

 solutions were determined after fungi had grown on them for 

 two weeks, and the results obtained indicate that there is no 

 definite relation between the active acidity produced by these 

 fungi and their ability to inhibit or stimulate the growth of an- 

 other. For example, in fig. 3, Pleurotus sapidus grew over 

 Aspergillus glaucus very rapidly, but was entirely inhibited by 

 A. versicolor on the solid agar medium. In the solutions Pleuro- 

 tus sapidus produced an active acidity of P H 5.4, while Aspergillus 

 glaucus and A. versicolor changed the active acidity to about the 

 degree P H 6.6 and P H 6.4, respectively; also, Trametes Peckii grew 

 over both Daedalea quercina and Aspergillus fumigatus, al- 

 though the change in active acidity produced by Daedalea 

 quercina was P H 3.0 and that produced by Aspergillus fumigatus 

 was P H 6.6. Many such examples could be cited by comparing 

 with table i the following active acidities produced by the fungi : 

 Lenzites vialis, P H 5.0; Merulius pinastri, P H 7.0; Daedalea quer- 

 cina, P H 3.0; Trametes Peckii, P H 4.2; Pleurotus sapidus, P H 5.4; 

 Merulius lacrymans, P H 5.0; Lentinus lepideus, P H 5.4; Daedalea 

 confragosa, P H 5.8; Coniophora cerebella, P H 5.4; Polystictus ver- 

 sicolor, P H 5.4; Isaria sp., P H 6.8; Polyporus lucidus, P H 5.4; 

 Polystictus hirsutus, P H 5.2; Aspergillus glaucus, P H 6.6; A. niger, 

 P H 5.8; A. fumigatus, P H 6.6; A. versicolor, P H 6.4; and A. Sydowi, 

 P H 6.8. The control solution upon which no fungi had grown 

 had an active acidity of P B[ 5.4. Of course, there are some in- 

 stances where similar effects could be correlated with similar 

 changes in hydrogen ion concentration; for instance, Trametes 

 Peckii is similarly influenced by both Aspergillus fumigatus and 

 A. glaucus. 



The fungi were also grown on a nutrient solution containing 

 the same ingredients as the agar previously mentioned. Since 

 certain of the Basidiomycetes used do not grow well upon liquid 

 media it was found desirable to add to the cultures sufficient 

 quartz sand, free from all soluble substance, so that a slope of 

 sand could be formed above the surface of the solution out into 



