1919] 



ZELLER AND SCHMITZ — MIXED CULTURES 187 



the mycelium of the two thoroughly intermixed, as fig. 12 in the 

 plate shows for Merulius pinastri. An exception to this general 

 ' condition is illustrated when two colonies of Aspergillus niger 

 grew together. At first there was an inhibition of growth as 

 shown by a straight line formed by the margins of the two 

 colonies. Later, however, the two colonies generally inter- 

 mixed. As table I shows, there was often an intermixing of the 

 mycelium of two different species. This may be explained by 

 the theory advanced by Clark 1 that many deleterious sub- 

 stances, which at certain concentrations retard growth, later 

 cause great acceleration of mycelial development in the re- 

 tarded cultures. 



Cases of stimulation of growth when two colonies came into 

 contact were comparatively rare, while cases of stimulation be- 

 fore contact occurred seldom indeed. However, examples of 

 both these types were observed. In many cases it is hard to 

 distinguish between true stimulation and a mere heaping up of 

 the mycelium due to mechanical hindrance. Figures 7 and 10 

 of the plate show a stimulation of Trametes Peckii in contact 

 with Daedalea quercina. At first there was a heaping up of the 

 mycelium, and this appeared to be a great stimulation of growth. 

 However, this may equally well be considered a mere increase in 

 the amount of aerial mycelium due to a mechanical hindrance of 

 the surface of the medium. A peculiar case of stimulated growth 

 of Daedalea confragosa is shown in fig. 1. It is not certain 

 whether this is caused by the presence of Merulius lacrymans or 

 some other factor. However, there does not seem to be any 

 valid reason why a stimulation by diffusion should not be ex- 

 pected as much as inhibition of growth by diffusion, as where 

 Lentinus lepideus and Aspergillus glaucus are mutually inhibited 

 before contact. In the latter case the colonies never came to- 

 gether. A slight stimulation of growth of Polyporus lucidus in 

 the neighborhood of Isaria is shown in fig. 4. 



It was noticed that the sporulation of certain of the Fungi 

 Imperfecti was influenced by the growth of other fungi. For 

 example, there seemed to be an increase in size and number 



1 Clark, J. F. On the toxic effect of deleterious agents on the germination and 

 development of certain filamentous fungi. Bot. Gaz. 28:289-327, 378-404. 1899. 



2 



