Jan. 14, 1918 Cultures of Wood-Rotting Fungi on A riificial Media 39 



Some of the most important criteria for distinguishing different but 

 closely related fungi are found in the first 10 or 15 days of the growth of 

 the subcultures, such as rapidity of growth, color changes in the myce- 

 lium, staining of the agar, decoloration of media, etc. Important char- 

 acters which are sharply defined at one stage of growth often disappear 

 or are obscured by the later mycelial development; and for this reason 

 the cultural data in the tables have been given for several periods of 

 time in the growth of the cultures, say at 10, 20, and 30 day intervals. 



INFlyUENCE OF SUNUGHT ON CULTURAI, CHARACTERS 



One of the special benefits which seems to be derived from exposing 

 cultures to the sunlight is the accentuating of the color characteristics 

 and toning down of the mycelial growth of the fungus, thereby making 

 it more characteristic and uniform for a given species than when placed 

 under similar conditions in the darkness. 



The differentiation of the characters of the mycelium produced, both 

 as to texture and color of the aerial mycelium, is very much more marked 

 when the cultures are grown in the presence of light at ordinary room 

 temperatures than when grown in incubators at the optimum and con- 

 stant temperature for the mycelial growth of the fungus under considera- 

 tion. This probably explains why no one up to the present time has 

 seriously attempted to differentiate the various species of wood-rotting 

 fungi by means of cultural characteristics alone. 



Furthermore, the cultures when grown in darkness and at a more 

 or less constant and high temperature overrun very rapidly the surface 

 of the agar in the tube, thus obscuring the real growth of the fungus as 

 observed in the cultures subject to daylight conditions. 



GROWTH OF WOOD-ROTTING FUNGI ON AGARS 



Texture. — In the growth of wood-rotting fungi on agars the fungus 

 as it spreads from the inoculum on to the surface of the slant proper 

 assumes certain well-defined stages in its growth, which may be roughly 

 divided into two general divisions: (i) Fungi whose advancing young 

 mycelial zone is appressed and (2) fungi whose advancing zone is downy, 

 felty, woolly, etc. There is but little real difference between these 

 two methods of growth, since as a rule the character of the mycelium 

 first to appear is appressed. If the true aerial mycelium, in contra- 

 distinction to that which is strictly prostrate on the surface of the agar 

 keeps pace in its growth with the appressed mycelium, the zone of growth 

 will be downy, felty, woolly, etc. If, on the other hand, the growth of 

 the strictly aerial mycelium is much retarded, the appressed mycelium 

 will present a well-defined zone from one to several millimeters across. 



The appressed mycelium is usually either colorless or both colorless 

 and sodden, and from this the true aerial mycelium usually develops. 

 The cottony mycelium as a rule does not persist in this condition for 



