1909] STEVENS & HALL—VARIATION OF FUNGI 7 
due to any one of many structural characters of the colony; to vary- 
ing density of spore massing, grouping of pycnidia, mycelial branching, 
color, etc. It is a frequent phenomenon in nature in the fairy rings 
of the toadstools, the concentric markings of many leaf spots, fruit 
rots, etc. These effects have been attributed to various causal 
agencies, to light relation,+ to nutrients,’ to agencies other than light, 
probably food, to resting periods (HEDGECOCK, /. c.), and to mycelial 
crowding.° 
ASCOCHYTA CHRYSANTHEMI STEVENS 
With the fungus in question the fact that the zones are not due to 
light or temperature relations is apparent from the fact that they do not 
coincide with the fluctuations of these two factors (jfig.6). In the 
colony shown, which is that of a plate culture kept at room tempera- 
ture, there was daily change from warm to cool, light to dark; yet the 
number of rings does not coincide with the number of these changes; 
moreover, zones were produced in precisely the same way on plates 
kept constantly in the dark as on plates kept all of the time in the light, 
and still the same on plates kept three days in the dark and then three 
days in the light. 
Microscopic examination shows that with this fungus the dark 
zone is due to a larger number of mycelial filaments, the light 
zone to a smaller number of threads, as is shown diagrammatically in 
jig. 7. It seems that with this fungus the dense crowding of the fila- 
ments, resulting from their repeated branching, inhibits growth either 
by the products of metabolism or exhaustion of nutriment. There is 
then a period of quiescence, followed by onward growth of a few 
scattered hyphae. As these outgrowing hyphae reach beyond the 
inhibiting influence, they branch repeatedly, until a new dense zone 
Motz, Emit, Ueber die Bedingungen der Entstehung der durch Sclerotinia fruc- 
tigena erzeugten Schwarzfaule der Aepfel. Cent. Bakt. 1 
Houtcuinson, H. B., Ueber Form und Bau der Kolonieen niederer Pilze. Cent. 
Bakt. 1'72:602. 
HeEpceEcock, G. G., Zonation in artificial culture of “-egsopeein uae and other 
fungi. Rept. Mo. Bot. Garden 17:115-117. pls. 13-16. 1 
5 MirBurn, THos., Ueber Aenderungen der Farben bei Pilzen und Bakterien. 
Cent. Bakt. eee 
6 IstvANFFI, E, Etud I giques sur le rot gris de la 
vigne. Ann. aaa Gas Ampél. Roy. Hougrais 1905: 183. 
