536 
Chaudhuri.—A Study of the Growth in 
shown uniform growth. Zones generally appear by the end of the second 
week, when an area of 45-50 mm. in diameter has appeared. Zones 
appeared at a lower temperature than 25 0 C. only when the Petri dishes 
were continuously lighted. Thus ordinary Petri dishes were kept at 2i°-23° C. 
under continuous illumination, with some plates covered with black paint to 
prevent the entry of light. Zoning appeared only in the illuminated dishes, 
t ig. 11. Two cultures of V. albo-atmm on Coon’s medium plus agar. That on the left was 
incubated at 22-5° C. and shows no zonation, that on the right at 25 0 C. and shows well-marked 
zonation. 
flG. 12. A cultuie of V. albo-alrum on corn-meal agar at 25 °C.; zonation is clearly visible. 
which definitely shows that it was the effect of light that brought about 
zoning at this lower temperature. Zones failed to appear in the dark even 
at 25 0 C. when the media was acidified to a pH of about 2-8, but the same 
medium produced zones when exposed to light. Normal Coon (pH 4-3) 
pioduces zones at 25 0 C., but these are not very prominent. Very marked 
zone formation takes place at 25 0 C. when a fourteen days stale medium 
(pH 5 ~ 5 ‘ 2 ) is us ed. It is the same for 2i°-23° C. in the light. At 25 0 C. in 
