18 BULLETIN 227, U. S. DEPARTMENT OF AGRICULTURE, 



In addition to the possibility, in some instances, of chemical 

 combinations between the preservative and the media, there will also 

 necessarily be a slight change in concentration, due to the drying 

 out of the media when held in Petri dishes for six to eight weeks. 

 Likewise, during this interval of time certain volatile constituents, 

 particularly the lighter oils, may escape from the media. 



In recording observations of the behavior of the fungi toward the 

 preservative, rapidity and amplitude of growth, together with any 

 other peculiarities in appearance, were noted, inspection being made 

 about once a week. 



| One very interesting feature of the tests was the development of 

 a "halo" around either the living or the dead transfers, or in advance 

 of the fungous growth on the check cultures. These halos differed in 

 appearance on the different preservatives, sometimes being lighter, 

 sometimes darker, than the surrounding medium. In order to deter- 

 mine whether the change was due to advance submerged hyphge, 

 several transfers were made from the halos to fresh sterile agar, but 

 as no living organisms were demonstrated by this test or by micro- 

 scopical examination to be present it appears to be an advance 

 physico chemical change in the media, arising, perhaps, from the dif- 

 fusion of enzyms from the transfer, as Kellerman (15) has recently 

 demonstrated for cytase produced in fungus cultures. 



DEVELOPMENT OF FOMES ANNOSUS AND FOMES PLNICOLA. 



IN NONTOXIC CHECK CULTURES. 



In the check cultures, Fomes annosus produces a rather compact 

 creamy growth (PL II, fig. 20, and PL IV, fig. 48), forming an abun- 

 dance of the characteristic conidia described by Brefeld. F. •pinicola 

 (PL I, fig. 4; PL III, fig. 31; and PL IV, fig. 40), on the other hand, 

 develops a fluffy, deep, white mycelium of considerably more rapid 

 growth than F. annosus. At 25° C, F. pinicola develops a radial 

 growth of 24 mm. in 9 days (average of 14 tests) and covers the plate 

 in 15 days (15 tests); F. annosus develops 15 mm. in 8f days (19 

 tests) and covers the plate in 20^ days (12 tests). 



IN CULTURES CONTAINING TOXIC SUBSTANCES. 



The rate of growth of each of these two fungi on toxic media is 

 usually considerably retarded, in many cases strongly so, as com- 

 pared with check cultures. In some instances where very low con- 

 centrations of certain substances are used, a stimulating effect is ob- 

 served, but this condition is reversed with increased concentrations. 

 The stimulated growth on zinc-chlorid concentrations when heated 

 in the pr; s nee of the culture media (such concentrations often being 

 far above those necessary to kill when not so heated together) is 



