535 
Culture of Verticilliuni olbo-atrum , B. et Br. 
the increase in surface area. Instead, there is approximately the same in¬ 
crement of weight for each period. This may be attributed either to the 
old mycelium ceasing to produce new growing hyphae or to the young 
mycelium, though increasing in amount, growing less and less vigorously. 
An experiment was carried out to throw some light on the action of 
aeration. Does it act by oxidizing the staling products or by reducing 
their production ? An experiment was started with a medium staled for 
thirty-five days which had been used for the non-aerated cultures and in 
which growth had stopped. The medium was filtered and put in flasks 
under aseptic conditions, and then inoculated and aerated for fifteen days. 
A similar set was left non-aerated. Very little growth took place in either, 
and the growth in the aerated (0-0034 + 0*0004 grm.) was not greater than the 
growth in the non-aerated ones (0-0036 + 0-0005 grm.). This indicates that 
aeration favours growth, not by oxidizing waste products, but by keeping 
down the production of waste products. 
Zone Formation by Ver ticillium albo-atrum. 
In connexion with the experiments in temperature, it was found that 
the fungus formed zones regularly at a certain temperature, viz. 25 0 C. in 
all media. Fig. 11 shows zonation in Coon’s medium with agar, and Fig. 12 
zonation in corn-meal agar. 
An attempt has been made to discover some of the conditions affecting 
ring formation. ‘ It has been studied in three different relations, viz. the 
medium, heat, and light. 
It has been mentioned before that this fungus always causes the medium 
to become alkaline. Coon’s normal, normal with 0-3 per cent. HC 1 , and 
normal with 0-3 per cent. NaOH, as well as Coon’s N/2, N/4, and a fourteen 
days stale liquid, were plated with agar. These were inoculated and in¬ 
cubated at 14 0 , 16 0 , 18 0 , 21 0 , 22-5°, 25 0 , and 26° C., but zones appeared at 
25 0 C. only, and the zoning in half-normal, quarter-normal, stale medium, and 
alkaline medium was more marked than in the others. Though the amount 
of growth at ]8° C. was the same as that of 25 0 C., no rings appeared at the 
lower temperature. A study of a graph showing the daily spread in an 
agar colony at the two temperatures exhibits the lines crossing and re¬ 
crossing many times, showing that the growths at these temperatures are 
the same. The total growths are also the same. If equal amounts of growth 
produce equal amounts of waste products, and staling products are the 
cause of zone formation, then we should expect rings equally at 18 0 C., as 
at 25 0 C. But no rings appeared at 18 0 C. 
The rings at 25 0 C. do not appear successively as growth proceeds, as 
in Penicillmm. The colony grows uniformly for a certain time, and then 
suddenly zones appear in the mycelium already formed, which had previously 
