537 
Culture of Verticil Incut aibo-atrum , B. ct Br. 
darkness and 2i°-23° C. lighted, ring formation is very marked when about 
3 per cent. NaOH is added (pH 7 ' 0 )- In connexion with zone forma¬ 
tion at a lower temperature in light, it is noteworthy that the rings do not 
appear suddenly as at 25 0 C. in darkness, but gradually one after 
another from the very beginning. The results now may be tabulated as 
follows: 
Medium. 2 2.5 0 C. 
21°—2 3 0 C. 
2I°-23°C. 
25 0 C. 
Darkness. 
Light. 
Darkness. 
Darkness. 
Coon’s normal — 
+ 
_ 
4 
Coon’s i normal — 
+ 
— 
4 
Coon’s f normal — 
+ 
— 
+ 
Coon’s 14 days stale — 
+ 
— 
4 
Coon’s normal with — 
0.3 % HC 1 
4 
— 
— 
Coon’s normal with — 
0.3 % NaOH 
4 
— 
4 
At 20 0 C. and below this temperature, light produced no zonation in 
any medium. 
We may now conclude that an alkaline medium favours ring formation 
(up to pH 7*o, or just over it), but if the medium becomes very alkaline 
(pH 8-o), as in a very stale six months old medium, the fungus grows, 
but no rings are formed. Also that in the dark zone formation is practi¬ 
cally confined to 25 0 C., which, however, can be lowered slightly by exposure 
of the culture to light. 
Zone formation has been held to be due to a periodic external factor, 
e.g. alternation of light and darkness; but in these experiments rings 
were formed not only in constant darkness but also under continuous 
illumination. 
It has been claimed that the production of staling substances is the 
cause of zone formation. Verticillium , however, grows best at 22-5° C., so 
should then form most waste products, yet no zones are formed in darkness 
at that temperature, although they appear under similar conditions at 25 0 C. 
The way in which the zones appear suddenly at 25 0 C. does not support the 
alkali diffusion theory of Munk ( 3 ). Also Moreau’s ( 4 ) view of alternation 
of light and darkness cannot be applicable as already stated. Hedgecock ( 5 ), 
in his experiments on zonation with Cephalothecium , found light to be the 
determining factor, and showed that variation of temperature did not cause 
zonation ; he showed also that no zonation occurred in darkness, and that 
light of different wave length had different actions on zone formation. 
Similar experiments were carried out by Knischewsky (6) with Penicillimn 
luteum . Munk ( 7 ) had also found that on exposure to light zonation 
develops, but not at constant temperature in darkness. He had found that 
increase in the amount of nutrient makes the zones narrower and tends to 
diminish coremium formation. 
Plates were grown at 25 0 C. with the medium 6 mm. and 12 mm. thick, 
